Modular ladar sensor

ABSTRACT

A lightweight, low volume, inexpensive LADAR sensor incorporating 3-D focal plane arrays is adapted specifically for modular manufacture and rapid field configurability and provisioning. The present invention generates, at high speed, 3-D image maps and object data at short to medium ranges. The techniques and structures described may be used to extend the range of long range systems as well, though the focus is on compact, short to medium range ladar sensors suitable for use in multi-sensor television production systems and 3-D graphics capture and moviemaking. 3-D focal plane arrays are used in a variety of physical configurations to provide useful new capabilities.

BACKGROUND

1. Field

The embodiments disclosed herein relate generally to 3-D imagegeneration and recording and more particularly to systems which maysynthesize 3-D solid object models from data supplied by multipleoptical sensors. Many systems have been proposed to meet the challengeof using video cameras in a production system to create 3-D maps ofscenes and models of solid objects. Stereo systems, holographic capturesystems, and those which acquire shape from motion, have all beenproposed and in some cases demonstrated, but what is lacking is a systemwith the capability of producing a full 360 degree solid object modelwithout a time consuming set up, and operating conditions which resultin restrictions on the actors, set, scene, athlete, or object in play.

2. References to Related Art

The 3-D imaging technology disclosed in Stettner et al, U.S. Pat. Nos.5,446,529, 6,133,989 and 6,414,746 provides with a single pulse oflight, typically pulsed laser light, all the information of aconventional 2-D picture along with the third dimensional coordinates;it furnishes the 3-D coordinates of everything in its field of view.This use is typically referred to as flash 3-D imaging in analogy withordinary digital 2-D cameras using flash attachments for a selfcontained source of light. As with ordinary 2-D digital cameras, thelight is focused by a lens on the focal plane of the LADAR sensor, whichcontains an array of pixels called a focal plane array (FPA). In thecase of a LADAR sensor these pixels are “smart” and can collect datawhich enables a processor to calculate the round-trip time of flight ofthe laser pulse to reflective features on the object of interest. Eachsmart pixel also collects data associated with the returning laser pulseshape and magnitude. The work of Stern and Cole, “High-sensitivity,wide-dynamic-range avalanche photodiode pixel design for large-scaleimaging arrays”, appearing in the Journal of Electronic Imaging 19(2),021102 (April-June 2010), is referenced for design features andfabrication techniques which may improve the efficiency and isolation ofthe elements of the focal plane detector arrays common to the severaldesigns described herein.

One value of these flash LADAR sensors, as opposed to competing designsin which one or more pixels is scanned over the field of view, is theelimination of the precision mechanical scanner, which is costly, highmaintenance and typically large and heavy. The pixels in the focal planeof a flash LADAR sensor are automatically registered due to theirpermanent positions within the array. Further, by capturing a frame ofdata as opposed to one or a few pixels with one laser pulse, the datarate is greatly increased while weight and volume are reduced. Becauseeach frame of data is captured from the reflection of a short durationlaser pulse, moving objects or surfaces of stationary objects may becaptured from a moving platform without blurring or distortion.

It is therefore desirable to provide a device to generate 3D data whichis both low cost and flexible in manufacture due in part to the modularnature of the design. It is also an object of the invention to provide amodular ladar sensor unit as a component which may be utilizedubiquitously in any application by any imaging platform, computer, orhost device provided with a number of basic electrical and mechanicalinterfaces. It is a further object of the invention to provide a flashladar sensor component to a 3-D video production system which is bothflexible and rapidly reconfigurable, allowing it to be adapted to anyfield of play, theater, arena or surveillance sector.

SUMMARY OF THE INVENTION

A modular ladar sensor employs a receiver module within housing. Thehousing incorporates a quick connect optical receptacle coupler and hasa laser transmitter electrical connector and a laser transmittermechanical mount for rapidly mounting a laser transmitter module. A lensassembly with a quick connect optical plug coupler mates with theoptical receptacle coupler. A laser transmitter module with anelectrical connector is adapted to engage and mate with the lasertransmitter electrical connector, and with complementary mechanicalmounting and fastening features mates with the laser transmittermechanical mount. The laser transmitter has a modulated laser lightoutput and a diffusing optic for illuminating a scene in the field ofview of the modular ladar sensor. A two dimensional array of lightsensitive detectors is positioned at a focal plane of the lens assembly,each of the light sensitive detectors with an output producing anelectrical response signal from a reflected portion of the modulatedlaser light output. A readout integrated circuit with multiple unit cellelectrical circuits, each of the unit cell electrical circuits having aninput connected to one of the light sensitive detector outputs, and eachunit cell electrical circuit having an electrical response signaldemodulator and a range measuring circuit connected to an output of theelectrical response signal demodulator, is connected to a referencesignal providing a zero range reference for the range measuring circuit.A detector bias circuit is connected to at least one voltagedistribution grid of the array of light sensitive detectors and atemperature stabilized frequency.

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a typical application of the present inventionadapted for rapidly mounting to a production video camera forbroadcasting a sporting event, and the use of multiple cameras andsensors to produce a composite 3-D image;

FIG. 2 is a system block diagram of a typical application as shown inFIG. 1 of the present invention of a modular ladar sensor of the typedescribed herein;

FIG. 3 shows a first type of a modular ladar sensor suitable for fastand easy external connection to field equipment through a cable adaptor;in this case a personal or professional video camera;

FIG. 4 shows a second type of a modular ladar sensor suitable for fastand easy external connection to field equipment through a quick mountelectrical and mechanical connector; the equipment in this case being apersonal or professional video camera;

FIGS. 5 A, 5B, 5C, and 5D show an exploded view, top view, clip detailand slot detail, respectively, of a modular ladar sensor unit forinternal mounting within a chassis and details features of the modulefor mating, retention within the chassis, and suppression of radiatingelectromagnetic fields;

FIG. 6 is a system block diagram of the modular ladar sensor and theinternal workings as well as external connections.

FIG. 7 shows a diagram of the unit cell electronics of the readoutintegrated circuit associated with each pixel of the detector array ofFIG. 6

FIG. 8 shows a block diagram of the components of an optional cablelength equalization system of a master controller operating within avideo production bay for a 3-D video production setup employing multiplevideo cameras and ladar sensors, and pertaining to the application shownin FIGS. 1 and 2;

FIG. 9 is a diagram of the wavelength multiplexer component which may beused to equalize the interconnect delay of an optical cable in anapplication requiring the combination of several ladar sensors, and whenprecision timing is required;

FIG. 10 is a diagram of a frequency multiplexer component which may beused to equalize the interconnect delay of an electrical cable in anapplication requiring the combination of several ladar sensors, and whenprecision timing is required;

FIG. 11 is a diagram showing the arrangement of a file formatincorporating essential elements useful in creating composite 3-D modelsfrom multiple ladar sensors, each with a 3-D image output.

FIGS. 12A and 12B are a diagram showing the modular attachment of theoptical subassembly and the laser transmitter subassembly to thereceiver body of the modular ladar sensor and a detail view of thebayonet receptacle feature for a lens;

FIG. 13 shows the construction of an improved focal plane array ofdetectors realized as an array of avalanche photodetectors on asilicon-on-sapphire or gallium nitride-on-sapphire substrate which maybe used in visible and near-IR applications of the modular ladar sensor;

FIG. 14 shows the construction of an improved focal plane array ofdetectors realized as an array of PIN photodetectors on asilicon-on-sapphire or gallium nitride-on-sapphire substrate which maybe used in visible and near-IR applications of the modular ladar sensor;

FIG. 15 illustrates the hybrid assembly of a focal plane array ofdetectors onto a readout integrated circuit of the present invention;

DETAILED DESCRIPTION

This application contains new subject matter related to previous U.S.Pat. Nos. 5,696,577, 6,133,989, 5,629,524, 6,414,746, 6,362,482,D463,383, and U.S. patent application Ser. No. 10/066,340 filed on Jan.31, 2002 and published as US 2002/0117340 A1, the disclosures of whichare incorporated herein by reference.

The embodiments disclosed herein provide a device for 3-D imaging usinga modular ladar sensor with a field of view and a wavelength ofoperation comprised of several components, wherein each of the keycomponents of the ladar sensor is a self contained sub-assembly, easilyassembled together to produce a functional ladar sensor. Each of themodules, or sub-assemblies, has both mechanical and electricalinterfaces well suited to modular assembly. The modular ladar sensor mayalso have an optical interface and connector. The modular ladar sensoris well adapted externally to be rapidly mounted to any equipment havinga proper set of external mechanical, electrical, and optical interfaces.The modular ladar sensor has an illuminating laser module which mayincorporate a semiconductor laser with a modulated laser light output,or a giant pulse solid state laser, and a diffusing optic forilluminating a scene in the field of view of the modular ladar sensor.The modular ladar sensor also comprises a receiver module featuring atwo dimensional array of light sensitive detectors positioned at a focalplane of a light collecting and focusing assembly. The light collectingand focusing assembly may also be modular, with a quick-connectmechanical interface. Each of the light sensitive detectors has anoutput producing an electrical response signal from a reflected portionof the laser light output. The electrical response signals are connectedto a readout integrated circuit with a corresponding array of unit cellelectrical circuits. Each of the unit cell electrical circuits has aninput connected to one of the light sensitive detector outputs, anelectrical response signal demodulator, and a range measuring circuitconnected to an output of the electrical response signal demodulator.The demodulator may be a voltage sampler and analog shift register forstoring sequential samples of the electrical response signals, or it maycomprise a mixer, integrator, or matched filter. The demodulation mayalso take place external to the readout integrated circuit, by a fastdigital processor operating on a sequence of digitized samples from eachpixel. The fast digital processor may employ algorithms which utilizeweighted sums of sequential analog samples, or use fast Fouriertransforms, convolution, integration, differentiation, curve fitting, orother digital processes on the digitized analog samples of theelectrical response signals. The unit cell may also incorporate atrigger circuit, set to produce an output response when the output ofthe demodulator exceeds a preset threshold. The range measuring circuitis further connected to a reference signal providing a zero rangereference for the modulated laser light output. The modular ladar sensorfurther incorporates a detector bias circuit connected to a voltagedistribution grid of the detector array and a temperature stabilizedfrequency reference.

As will be shown and described with respect to the drawings, the instantinvention is modular in two respects; first in the assembly of the ladarsensor component sub-assemblies, and second in the ubiquitous mannerwhich the quick connect interfaces provide 3-D image sensing to any hostplatform having the mating interfaces. The present invention is acompact modular ladar sensor embodied in a modular assembly of a lasertransmitter, optics sub-assembly, and camera body with internal receivermodule. The modular ladar sensor is provided with an external quickconnect mechanical and electrical interface for rapid mounting andde-mounting to a host platform, thus providing 3-D sensing capability toany host platform having the complementary electrical and mechanicalquick connect interfaces. In some cases, the modular ladar sensor isadapted to plug into a quick connect mechanical and electrical interfacemounted on an outside surface of the host platform. In other cases, themodular ladar sensor is adapted to plug into a quick connect mechanicaland electrical interface mounted inside a surface of the host platform.In some instances, the quick connect mechanical and electrical interfaceincludes a fiber optic connector. In a further development, the modularladar sensor is realized as a compact ladar sensor unit, streamlined tofacilitate plugging and unplugging of the unit onto the surface of ahost equipment, or into a recess of a host equipment.

The modular ladar sensor may include a system control processor withfrequency reference and inertial reference, a system memory, a pulsedlaser transmitter, transmit optics, receive optics, an array of lightdetecting elements positioned at a focal plane of the receive optics, adetector bias converter for supplying bias voltage to the lightdetecting focal plane array, a readout integrated circuit,analog-to-digital converter circuits for producing digital image datafrom the analog readout IC outputs, a data reduction processor foradjusting and correcting the image data, and an object trackingprocessor for identifying and tracking features and objects in thecorrected image database. When used with feedback and controlmechanisms, a tracking 3-D video production of moving objects isenabled, and in a wide array of other mobile equipment, collisionavoidance, scene capture, guidance, and navigation is enabled.

Each pixel in a 3D focal plane array (FPA) converts impinging laserlight into an electronic signal whose magnitude is sampled in time andstored in memory within the pixel. Each pixel also uses a clock to timethe samples being taken in response to the captured reflection of thelaser light from a target surface. Different embodiments may includebayonet mounted receiving optics, a special purpose reduced instructionset computing (RISC) processor, an array of vertical cavity surfaceemitting lasers, an array of laser diodes, or an optically pumped solidstate laser, and an FPA of light detecting elements formed on asilicon-on-sapphire (SOS) or gallium nitride on sapphire substrate(GNOS), and the light detecting elements may be avalanche photodiodes(APDs), PIN diodes, or NIP diodes. The modular ladar sensor may alsohave special provisions for reducing the EMI radiated from a hostplatform chassis which has an opening adapted to accept an internallypluggable modular ladar sensor of the type described herein. There maybe an EMI gasket, a spring loaded door, and spring fingers mounted to anopen cage structure similar to the GBIC cage described in design patentD463,383. The cage structure may have integrally molded guide rails and“J” hooks for connecting to a host platform printed circuit board orenclosure panel. The cage structure may also mount an electrical/opticalconnector at a rear opening, or the electrical/optical connector may bemounted to a PC board of the host platform in a preferred embodiment.The modular ladar sensor typically incorporates a hybrid assembly offocal plane array and readout integrated circuit, and the readout IC isarranged as an array of unit cell electrical circuits, and each unitcell is arranged to be in an array of identical spacing and order as themating focal plane array.

The unit cells of the modular ladar sensor may also make use of amatched filter incorporating a parametric analog correlator, and may usechirped transmissions or multi-pulse transmission codes such as Barkercodes, to deal with multipath reflections from objects or features inthe field of view of the modular ladar sensor, and to produce processinggains. The modular ladar sensor may also make use of pulsed CWtransmissions and heterodyne detection to enhance range performance asdescribed in the reference material. The modular ladar sensor is welladapted by a variety of innovative features and structures to bemanufactured efficiently and rapidly deployed in the field by externalor internal recessed pluggable mounting to any electronic host platformhaving the requisite electrical, mechanical, and optical interfaces. Themodular ladar sensor is specifically adapted to a lightweight, lowvolume, low cost design, which provides new capabilities when applied toa variety of imaging applications. The modular ladar sensor in a firstembodiment is capable of working in a flash mode as described above, orin a multi-pulse mode, or in a pulsed continuous-wave mode as thesituation dictates.

The production system incorporating the modular ladar system has anumber of features which enable full 3D object modeling and tracking, aswell as scene enhancements derived from the merging of 2D and 3D databases and managing of both 3D and conventional 2D video cameras. Theproduction system also has the ability to null differences in lengthbetween the various connecting cables of the deployed system, whetheroptical or electrical, and the ability to self-locate globally a mobileproduction van or edit bay, as well as the ability to project a localcoordinate system wirelessly to the various cameras deployed in aparticular venue.

The first embodiment of the modular ladar sensor includes a “D”connector plug having electrical connecting pins and a metal shell andflange with retained jackscrews for attaching to a host platform. Anarray of vertical cavity surface emitting lasers provides pulsedilluminating energy to a scene in the field of view at an eye-safewavelength. The first embodiment provides a 128×128 array of lightdetecting elements situated on a single insulating sapphire substratewhich is stacked atop a readout integrated circuit using a hybridassembly method. In other embodiments of the design, M×N focal planearrays of light detecting elements with M and N having values from 2 to1024 and greater are anticipated.

The compact design using modular receive optics and laser transmittersub-assemblies with highly efficient surface emitting semiconductorlasers, creates an opportunity to incorporate 3-D ladar imagingcapability into a variety of portable and professional electronicequipment, including video cameras, robotic crawlers, automobiles,trucks, airplanes, boats, portable computers, and a variety of imaginginstruments. Other applications can be envisioned for such a compact andcost effective design as is described herein in the preferred andalternative embodiments, and a more exhaustive list is presented insucceeding paragraphs.

A first embodiment of the modular ladar production system, is depictedin isometric drawing form in FIG. 1. A production van 2 controls thefunctions of the major components of the production video system.Production van 2 receives global positioning coordinates and timereferences from GPS satellites and transmits video via receiving andtransmitting antenna 4 mounted to the top of the production van or truck2. A local positioning coordinate system uses local antenna 6 totransmit local positioning references and may receive responses fromother camera antennas 16, 30 mounted to modular ladar sensors 14 or tothe host video camera platform. Production van 2 also connects to aprofessional video camera 12 through bidirectional fiber optictransmission link over fiber optic cable 8. Professional video camera 12is mounted to a wheeled dolly and rests on a dedicated platform 10projecting from stadium or arena structure 44. Modular ladar sensor 14is mounted externally to professional video camera 12 through a “D” typeelectrical connector and secured with jackscrews as shown in the detailof FIG. 4. A GPS receiving antenna 16 may be mounted to video camera 12or modular ladar sensor 14, and receives position and time referencedata from satellites or other local references such as production van 2.The GPS receiving antenna 16 may also be used to transmit camera statusor video signals back to production van 2 if suitable fiber optic orelectrical cable connections are unavailable. Professional video camera12 and modular ladar sensor 14 are typically set up to view at minimumthe entire playing surface of the field within the boundary lines 18,but may have a wider or narrower field of view depending upon the numberand type of cameras employed in the production. Of primary importance,professional video camera 12 and modular ladar sensor 14 are set up witha clear view of a regular feature 20, in this case a goalpost, which mayin general be any feature of the field or stage of the scene, such as aend zone flag or pylori, home plate, pitcher's mound, blue line inhockey, net of a tennis court, actor's marks, set, scene, or backdropfeatures of a play or studio, or any other identifiable and stationaryfeature of the set, scene, court, or field of play. An object in play22, in this case a football, travels within the field of play, court,stage, or set, and may be tracked by any of the professional videocameras 12, 28, 32, or 38. The stadium 44, arena, studio, or set, has astanchion 24 or other vertical support member providing an overheadpoint of attachment for a plurality of traversing cables 26 whichsupport SkyCam® 28, or other mobile overhead camera system 28, whichalso has embedded a modular ladar sensor unit 29 according to thedrawings of FIG. 5A-D. The mobile overhead camera 28 also has an antenna30 which may be used to transmit and receive GPS or local positioningreference data, camera status, and movement control commands from theproduction van 2. These signals may also be transferred bidirectionallyover electrical cable or fiber optic link 31 which may be strungvertically along stanchion 24 and then along traversing cables 26 orembedded within traversing cables 26.

A second professional video camera 32 with modular ladar sensor 14 ismounted on a second platform at a far end of stadium 44 and communicatesbidirectionally through fiber optic cable 34 to production van 2 and ismounted atop a wheeled dolly and is sited to cover the shadows or blindspots seen from the first professional video camera 12. A third fiberoptic or electrical cable 36 connects a third field level professionalvideo camera 38 with a third modular ladar sensor 14 and local antennamounted thereto to production van 2. Third professional video camera 38is mounted on a wheeled cart 39 which travels on a fixed track 40 inmanner similar to a railroad car. All three professional video camerasmay also used to track athlete/actor 42 as he/she travels from point topoint in the field of play, set, stage, or court. The actor/athlete 42may have a special feature such as a football helmet, hat, coat, shirt,shoes, or gloves attached which may have special infrared reflectorsinstalled to enhance the tracking thereof. The applied reflectorsincrease the levels of the reflected light pulses from theathlete/actors 42 and objects in play 22, thus enhancing the accuracy of3D range data, and making it easier to separate the actor/athletes 42and objects in play 22 from the background, and thus make the trackingof these actor/athletes 42 and objects in motion 22 much easier. Theseinfrared reflectors may be a decal or special reflective film applied tothe athlete's helmet, and which are otherwise transparent to lightexcept at the wavelength of interest, in this case 1.57 micron pulsedlight emitted from the modular ladar sensors 14. Installation of thesereflectors may also be effected on the object in play 22 to enhancedetection and tracking of the object in play, which in the case of abaseball, hockey puck, or golfball, may be very difficult to trackvisually using only 2-D data. Any object in play 22 or special featureof an actor/athlete's 42 costume, uniform, or equipment may also becoated with a reflective film by placing the object in a physical vapordeposition (PVD) chamber and applying a series of coatings byevaporation, flame spray, sputtering, or gas decomposition. Use of theinfrared reflector films or decals may allow for more effective ladarenabled tracking without altering the appearance of the actor/athletes42 or objects in play 22, since the wavelength of interaction is beyondthe visible spectrum. Use of multiple 2D professional video cameras 12,28, 32, and 38 and modular ladar sensors 14, 29 provides a 3D visionsystem that allows for a complete color 3D model of theactor/athlete/performer 42, object in play 22, regular features 20, andfield of play, set, stage, or court within a boundary 22 to be composedby a 3-D scene processor within production van 2. The individualprofessional video cameras may be commanded to point in any directionwithin their field of view by commands sent from production van 2, ormay be set in a remote tracking mode, wherein the modular ladar sensor14 output 3-D data is fed to the servo control motors of professionalvideo camera 12, and the servo motors of professional video camera 12controlling azimuth, elevation, and the zoom lens drive may be used totrack and frame the object in motion 22, or actor/athlete/performer 42.The preferred embodiment of FIG. 1 has the modular ladar sensors 14attached to professional video cameras 12 which produce conventional 2-Dvideo, but the modular ladar sensors 14 may be operated independently ofany 2-D video camera 12, instead mounted to or within a basic hostplatform consisting of a simple open frame computer, embedded computer,controller, or dedicated electronic circuits housed in a simpleelectronic enclosure.

FIG. 2 is a block diagram of the installation of the modular ladarsensor production system shown in FIG. 1, and showing a number ofadditional features. Production van 2 has a master control console 46which controls each of the cameras in the production suite, receives 2Dand 3D video feeds from each camera system, and broadcasts localpositioning data through local antenna 6, and may receive wirelesssignals in return from one or more of the professional video cameras 12,28, 32, or 38. In the installation of FIG. 1, master control console 46transmits commands to 3D camera system 1 made up of professional videocamera 12 and modular ladar sensor 14 through fiber optic cable 8. 3Dcamera system 1 (12, 14) is mounted atop a first wheeled dolly 50. Thepointing, focusing, and framing (zoom) of camera system 1 may beeffected by a human operator, or may be done by servo motors controlledby a local digital controller residing on professional video camera 12.Inputs to the local controller residing on professional video camera 12may come from master control console 46, or may come from modular ladarsensor 14 which may be tracking an athlete/actor/performer 42, object inplay 22, or some identifiable feature 20 in the field of play 18, suchas a goal post, net, pylori, or prop. Master control console 46 alsoreceives camera status data and 2D and 3D video signals from 3D camerasystem 1 via fiber optic cable 8. Master control console 46 also has ascene processor, capable of accepting 3-D range and intensity files, aswell as conventional 2-D video files and still pictures, from multiplesources simultaneously, and of using both the 3-D and 2-D data tocompose and refine a solid model of an object of interest or scene inthe common field of view of the multiple camera sources. Typical framerates for 3D camera system 1 (12, 14) are in the range of 15-30 framesper second, allowing for time division multiplexing of transmit andreceive signals over fiber optic cable 8. There is sufficient timebetween frames to transmit 2D and 3D data from 3D camera system 1 (12,14) along with any requested camera status information, and to receivecontrol commands from master control console 46. For example, if a 1Mpixel camera were to use 24-bit color representation (R,G,B) and a12-bit range and 8-bit infrared intensity representation, a typicaluncompressed 3D frame would be on the order of 5.5 Mbytes. Only 44Mbits/frame is required given this type of representation. Given amodest 1.25 Gigabit Ethernet connection, and a 20 Hz full frame ratevideo, then only 880 Mbits of the 1000 Mbit payload of the GigabitEthernet standard connection would be used, leaving plenty of time foran uplink containing camera commands to be sent. If a losslesscompression is used on the 3D data frame, a 2:1 compression may berealized, enabling frame rates of up to 40 Hz, while still accommodatinga camera control uplink signal from master control console 46. In thealternative, where frame rates must be higher, or image pixel countsgreater, a wavelength division multiplexing scheme may be used to divideuplink and downlink, or to double or triple the number of downlinks ifdesired. The wavelength division multiplexing hardware is detailed inFIGS. 9 and 10. Of course, simply increasing transmission rates bymoving to 2× Fibre Channel (2.125 Gbits/s), 4× Fibre Channel (4.25Gbits/s), 8× Fibre Channel (8.5 Gigabits/s), or 10 Gigabit Ethernet(loGigabits/s) will also yield excellent results at low cost, withoutresorting to complex wave division multiplexing schemes. Over shorterdistances, electrical connections over coaxial cable, twinax, or twistedpair may be used to connect master control console 46 bidirectionally toany of the 3D camera systems 1-3. These electrical connections may useEthernet signaling standards, Fibre Channel signaling standards, orother popular serial transmission standards, and may be transformercoupled or capacitively coupled, and may make use of time divisionmultiplexing to send camera command and control signals upstream frommaster control console 46. An alternative embodiment uses a frequencydivision multiplexing scheme as shown in FIG. 10. to create a separatecommand and control uplink from master control console 46 to 3D camerasystem 1 (12, 14) using the same shared physical media.

Continuing with FIG. 2, production van 2 also has a Global PositioningSatellite receiver 48 and antenna 4 for precisely determining theposition of the production van 2. The position of production van 2 maybe accurately and precisely established in the alternative bytriangulation from surveyor's marks or positioning thereon. Mastercontrol console 46 also connects to a SkyCam® overhead mobile camera 28which has an internally mounted modular ladar sensor unit 29 of the typeshown in FIG. 5A-D. A bidirectional fiber optic link via fiber opticcable 31 connects between master control console 46 and 3D SkyCam®overhead mobile camera 28. The mobile overhead camera 28 may be aSkyCam® or other brand, and will typically have at minimum an inertialreference, pointing and positioning servo motors, and a stabilizationcontroller, as well as all of the standard features of a typicalprofessional video camera. The 3D sky camera 28 is typically suspendedover the field of play/stage 18 by a system of traversing cables 26suspended from stanchions 24 or other vertical support feature ofarena/stadium/set 44. A second 3D camera system (32, 14) is mounted atopa second wheeled dolly 50 and connected via a second bidirectional fiberoptic link and fiber optic cable 34. Use of a second 3D camera system(32, 14) allows for a major reduction in shadows where no 3D pixelswould otherwise be measureable, owing to the single point of activeillumination provided by a system where only a first 3D camera system(12, 14) might be available. A third 3D camera system (38, 14) ismounted atop a tracked dolly 39 and connected via a third bidirectionalcommunications link, in this case an electrical cable 36. Use of a third3D camera system (32,14) allows for further reduction in shadows whereno 3D pixels would otherwise be measureable, owing to the dual points ofactive illumination provided by a system where only two 3D camerasystems (12, 14) & (32, 14) might be available. The use of a trackeddolly 39 and rails 40 allows the 3D camera system to be rapidly movedalong the major axis of the action, as in a scoring football play, fromgoalpost to goalpost 20. This ability to rapidly track a moving playallows for a much higher resolution 3D picture to be maintained in theinstances where the distance from a high mounted first or second 3Dcamera system (32, 14) such as platform 10 may mean only reducedresolution 3D images would be available for scoring events at or near anopposing goalpost 20 as in the scoring field goal kick shown in thediagram of FIG. 1. 3D sky camera 28 is an example of an overhead mobilecamera, and may be considered the fourth 3D camera system of thisexample, combining the advantages of rapid traversing with a uniquehigh-angle perspective not available in any other type of fixed platformor mobile tracked installation. Any of the 3D camera systems 1-4 may beconnected via electrical cable as opposed to fiber optic cable, orwirelessly, depending on many factors, including frame rate, distance,and EMI environment, without changing the nature or benefits of theinvention as described. Fiber optic links are preferred due to theirhigh data security, low loss, high bandwidth, low radiated EMI levels,low EMI susceptibility, reduced weight & volume, and ease of deployment.The system as described in FIGS. 1 & 2 may also be used in surveillanceapplications, with the surveillance space covered by any number ofcameras of both the 2D and 3D variety, together with those of combinedcapability. In surveillance applications, the ability to rapidly upgradeto 3D video is of major value, and the modular ladar sensor 14 or 29 isexpected to find many such applications where high value targets ordefensible spaces are being surveyed and monitored.

FIG. 3 shows a modular ladar sensor 14 of a type quickly connectablethrough an external cable assembly to a host platform, in this case aprofessional video camera 12. Professional video camera 12 has a DB-25electrical connector receptacle with a metallic shell 52 and bosses 54attached securely to an exterior surface by sheet metal screws, rivets,clips, or other fastener (fasteners not shown). Bosses 54 are drilledand tapped to accept a jackscrew 58 which may have a Phillips head, slothead, or socket head screw. A cable assembly with a plug at a first endconnects to the DB-25 electrical connector receptacle (52, 54) of theprofessional video camera 12. Jackscrew 58 is retained in flange 60 ofthe mating DB-25 connector plug, typically by a sheet metal clip. TheDB-25 connector plug has a metallic shell 56 with flanges 60 forsecuring the DB-25 connector plug to the chassis of the professionalvideo camera 12. The DB-25 connector is a pin-and-socket connector with25 mating pin/socket pairs, with the pins typically retained in the plugand the sockets retained in the receptacle. The back end of each pintypically has a solder cup or crimp style ferrule where individualinsulated wires 66 may be soldered, crimped, or permanently affixed byother method. A bundle of 25 insulated wires 66 within the dotted lineboundary 68 may be overmolded in a flat ribbon style or circular cablestyle, or may be left loose, placed in a loose tube sheath, or coveredwith a heat-shrink tubing and heat cured. Only 8 insulated wires 66 areshown in the drawing for the sake of clarity. A flexible rubber orpolymer strain relief 70 is overmolded onto the back of connector shell56 and the solder or crimp joints between the individual pins of theDB-25 connector and wires 66. The cable assembly is completed by asecond DB-25 connector plug at a second end comprised of the samecomponents as the first end. The DB-25 connector plug at the second endof the cable assembly connects to a DB-25 electrical connectorreceptacle which has a metallic shell 52 and bosses 54 permanentlyattached to an exterior panel of the modular ladar sensor 14. Modularladar sensor 14 also has a bayonet style optical mount 62 for receivinga modular lens assembly 64 with the mating bayonet fitting. In somecases, one or more of the insulated wires 66 of the cable assembly maybe replaced by an optical fiber cable, and the electrical pin and socketpairs of the DB-25 electrical connector plug and receptacle alsoreplaced with the proper ferrules, split sleeves, or precisioncylindrical fittings of an optical connector pair. The modular ladarsensor 14 receives power and ground connections from a host platform(video camera 12 in this case) through the DB-25 connector as well ascommand and control signals from a controller on the host platform. Themodular ladar sensor 14 also returns 3D data and internal status signalsto a controller on the host platform (video camera 12 in this case).

FIG. 4 shows a modular ladar sensor 14 of a type quickly connectablethrough a DB-25 electrical connector mating pair to a host platform, inthis case a professional video camera 12. Professional video camera 12has a DB-25 electrical connector receptacle with a metallic shell 52 andbosses 54 attached securely to an exterior surface by sheet metalscrews, rivets, clips, or other fastener. The “D” shaped connector is atype of “keyed” connector, which ensures the plug and receptacle mayonly be mated in the proper orientation. The metallic shell 52 providesEMI shielding as well as a surface at ground potential, which allows forcontrolled impedance electrical transmission through the connector. Theconnector receptacle fasteners are typically interior to the videocamera housing 12, and are not shown. Bosses 54 are drilled and tappedto accept a jackscrew 58 which may have a Phillips head, slot head, orsocket head screw. Jackscrew 58 is retained in flange 60 of the matingDB-25 connector plug, typically by a sheet metal clip. The DB-25connector plug is permanently affixed to an exterior surface of modularladar sensor 14, and has a metallic shell 56 with flanges 60 for quicklysecuring the DB-25 connector plug to the chassis of the professionalvideo camera 12. The DB-25 electrical connector pair is a pin-and-socketconnector with 25 mating pin/socket pairs, with the pins typicallyretained in the plug and the sockets retained in the receptacle. Theback end of each pin of the DB-25 connector plug protrudes into theinterior of modular ladar sensor 14, and typically has a printed circuitboard right angle or straddle mount connector. The back end of each pinof the DB-25 connector plug may alternatively have a solder cup or crimpstyle ferrule where individual insulated wires may be soldered, crimped,or permanently affixed by other method. The DB-25 connector plug mountedto the modular ladar sensor 14 in the drawing of FIG. 4 connects to theDB-25 electrical connector receptacle of the professional video camera12 which has shell 52 and bosses 54 permanently attached to an exteriorpanel. For a modular ladar sensor 14 with moderate size and weight, theDB-25 electrical connector plug and receptacle pair provide bothelectrical connection and mechanical support and retention. Modularladar sensor 14 also has a bayonet style optical mount 62 for receivinga modular lens assembly 64 with the mating bayonet fitting. In somecases, one or more of the electrical pin and socket pairs of the DB-25electrical connector plug and receptacle may be replaced with the properferrules, split sleeves, or precision cylindrical fittings of an opticalconnector pair. The modular ladar sensor 14 receives power and groundconnections from a host platform (video camera 12 in this case) throughthe DB-25 connector as well as command and control signals from acontroller on the host platform. The modular ladar sensor 14 alsoreturns 3D data and internal status signals to a controller on the hostplatform (video camera 12 in this case).

FIG. 5A shows a variant of the modular ladar sensor 14 as a modularladar sensor unit 29 which is adapted for plugging into a recessedcavity within a host platform such as SkyCam® 28 or professional videocamera 12. A recessed cavity in professional video camera 12 has anopening 116 defined by a cutout in a front panel 74 of the housing 118of professional video camera 12. Shown in FIG. 5A, housing 118 istypically formed of bent sheet metal for industrial use cameras, or maybe a zinc or aluminum casting for high end video production cameras, ormay be formed of an injection molded high impact plastic for consumergrade cameras. In any case, housing 118 must also serve as an electronicenclosure, and must contain any electromagnetic interference (EMI)signals radiated by the high speed electronics of the ladar sensor 29 aswell as the 2-D imaging electronics of the professional video camera 12.This requires the housing 118, to be conductive, and bent sheet metal,metallic castings, and molded plastic housings 118 must have conductivesurfaces either from metallic plating, applied chemical films such aszincate or chromate processes, or evaporated metallic coatings appliedunder vacuum in the case of a plastic molded housing 118. Alternatively,the housing 118 may be formed of a conductive plastic or conductivecarbon fiber, though a conductive surface may still need to be appliedin the form of electroless plating, electroplating, physical vapordeposition, sputtering, or flame spray. Front panel 74 also hasretention features 120 which may be tapped holes, ¼ turn fasteners, orsnap features situated so as to mechanically secure modular ladar sensorunit 29 within the recessed cavity defined by opening or cutout 116.Also shown in FIG. 5A is an aspect of guide slot 104 where it appearsnear opening 116. Dashed line AA shows the mating or plugging axis ofmodular ladar sensor unit 29, shown with either an integrated singleoptic 100, or as a module incorporating independent transmit optics 78and receive optics 76. The modular ladar sensor unit 29 shown with asingle integrated optic 100 features a mounting panel 60 and guide beams84 on either side of the package designed to engage with the matingguide slots 104 at either side of opening 116. If the professional videocamera is operated without a modular ladar sensor unit 29 in place, aconductive cover plate 98 is secured with screws 58 mating to tappedholes 120 in front panel 74. A conductive gasket 96 made of silver wiremesh, conductive elastomer, or deformable soft metal is typicallysandwiched between cover plate 98 and front panel 74 to ensure a lowleakage EMI seal. The modular ladar sensor unit 29 which featuresindependent receive optic 76, and transmit optic 78 is shown with guidebeams 84 and an optional quick connect retention feature 92 which isshown in greater detail in FIG. 5C. Within dashed circle BB is shown aside of modular ladar sensor unit 29 with a boss 94 securing andreceiving contoured leaf spring 92, which is bent so as to snap into thecross section of front panel 74 and be retained there. The retentionfeature 92 may be a contoured leaf spring as shown, or may be a screw, ¼turn fastener, snap or other convenient mechanism which interacts withthe mating retention feature 120 of housing 118 without altering theintent or beneficial effects of the instant invention. FIG. 5A shows avisible lens system 72 attached to professional video camera 12, whichmay be a fixed lens, zoom lens, or diffractive optic. Molded guide rail102 incorporates guide slot 104 and is also shown in FIG. 5D integrallymolded within plastic cage 106. Cage 106 has “J” hook features 108designed to affix the cage 106 assembly to a support structure. Cage 106may also have conductive EMI spring fingers 110 attached and a springloaded conductive door 112 with pivots 114 assembled thereto. The “J”hooks 108 are designed to snap into openings in a supporting structuresuch as printed circuit board 80 shown in FIG. 5B. The spring fingers110 are designed to both brush against a conductive surface of modularladar sensor unit 29 in the interior space of cage 106, and to pressagainst the edges of opening 116 in front panel 74, making a continuousconductive path from modular ladar sensor unit 29 to front panel 74 ofelectronic enclosure 118. Conductive door 112 makes the housing 118 intoan EMI sealed electronic enclosure whenever modular ladar sensor unit 29is not inserted into the professional video camera 12. The outersurfaces of modular ladar sensor unit 29 must be conductive in selectedareas and may be a cast aluminum or zinc housing plated with a thinprotective layer of copper, nickel, silver, chrome, gold, or othersuitable metal. The housing of modular ladar sensor unit 29 may also bemolded from plastic and electroplated, or coated with stainless steel ina PVD vacuum process, or coated by flame spray, RF assisted sputtering,or may alternatively have a formed metal sheet or foil applied andsecured with adhesive, clips, crimping, or other cold forming technique,or secured by reflowing part of a previously molded plastic feature. Thepivots 114 are spring loaded when inserted into the assembly of cage 106so conductive door 112 is pressed securely against the interior surfaceof front panel 74 when the modular ladar sensor unit 29 is not insertedinto the host platform. When a modular ladar sensor unit 29 is inserted,conductive door 112 swings inward and upward, allowing for the modularladar sensor unit 29 to be guided inward along guide rails 102 andplugged into a recessed connector such as the “D” style connector withshell 52 and mounting flange 86 shown at the rear of cage assembly 106in FIG. 5D. Guide rails 102 may alternatively have guide beams 84, andmodular ladar sensor unit 29 may have a guide slot 104 formed thereon,or any combination of rails and slots may be used on modular ladarsensor unit 29 and within cutout 116 of housing 118 without appreciablyaltering the operation or benefits of the instant invention.

FIG. 5B shows a plan view with modular ladar sensor unit 29 mounted to ahost circuit board 80 of professional video camera 12. Not shown is thecage assembly 106, but attachment points 82 are shown which may be slotscut in the PC board material to accommodate the “J” hooks 108 of themolded cage 106. A “D” style connector receptacle with shell 52 andflange 86 is mounted to the PC board by screws 88, and right angleconnector pins 90 solder to plated through holes of PC board 80, makingelectrical connections between the host platform and the modular ladarsensor unit 29. “D” style electrical connector plug with shell 56 at therear of modular ladar sensor unit 29 makes electrical connections withthe mating “D” type connector receptacle mounted to the PC board withguide beams 84 (shown in profile) engaging with the guide rails 102 asshown in the other views of FIG. 5A-D. A cross section of front panel 74shows interior bosses 54, which may be threaded nuts spot welded to theinside of front panel 74, and which receive jack screws 58. Jack screws58 mount through clearance holes in flange 60 of modular ladar sensorunit 29, and secure it mechanically to a host platform, in this caseprofessional video camera 12. The quick connect and disconnect featuresdetailed within dashed line circle BB may be used at either side ofmodular ladar sensor unit 29 as an alternative mounting method to thejack screws and retaining nuts shown in FIG. 5B. The modular ladarsensor unit 29 receives power and ground connections from a hostplatform (video camera 12 in this case) through the DB-25 connector aswell as command and control signals from a controller on the hostplatform. The modular ladar sensor unit 29 also returns 3D data andinternal status signals to a controller on the host platform (videocamera 12 in this case).

The major functional elements of modular ladar sensor unit 29 (or themore generalized modular ladar sensor 14), are depicted in block diagramform in FIG. 6. A control processor 122 controls the functions of themajor components of the modular ladar sensor unit 29 or modular ladarsensor 14. Control processor 122 connects to pulsed laser transmitter124 through bidirectional electrical connections (with logic, analog todigital (A/D) and digital to analog (D/A) converters 121) which transfercommands from system controller 122 to pulsed laser transmitter 124 andreturn monitoring signals from pulsed laser transmitter 124 to thesystem controller 122. A light sensitive diode detector (Flash Detector)123 is placed at the back facet of the laser so as to intercept aportion of the laser light pulse produced by the pulsed lasertransmitter 124. An optical sample of the outbound laser pulse takenfrom the front facet of pulsed laser transmitter 124 is routed to acorner of the detector array 130 as an automatic range correction (ARC)signal, typically over a fiber optic cable. The pulsed laser transmitter124 may be a solid-state laser, monoblock laser, semiconductor laser,fiber laser, or an array of semiconductor lasers. It may also employmore than one individual laser to increase the data rate. In an exampleembodiment, pulsed laser transmitter 124 is an array of vertical cavitysurface emitting lasers (VCSELs). In an alternative embodiment, pulsedlaser transmitter 124 is a disc shaped solid state laser of erbium dopedphosphate glass pumped by 976 nanometer semiconductor laser light.

In operation, the control processor 122 initiates a laser illuminatingpulse by sending a logic command or modulation signal to pulsed lasertransmitter 124, which responds by transmitting an intense pulse oflaser light through transmit optics 126. In the case of a solid statelaser based on erbium glass, neodymium-YAG, or other solid-state gainmedium, a simple bi-level logic command may start the pump laser diodesemitting into the gain medium for a period of time which will eventuallyresult in a single flash of the pulsed laser transmitter 124. In thecase of a semiconductor laser which is electronically pumped, and may bemodulated instantaneously by modulation of the current signal injectedinto the laser diode, a modulation signal of a more general nature ispossible, and may be used to great effect as is illustrated in thediscussions with respect to FIG. 7. The modulation signal may be aflat-topped square or trapezoidal pulse, or a Gaussian pulse, or asequence of pulses. The modulation signal may also be a sinewave, gatedor pulsed sinewave, chirped sinewave, or a frequency modulated sinewave,or an amplitude modulated sinewave, or a pulse width modulated series ofpulses. The modulation signal is typically stored in on-chip memory 125as a lookup table of digital memory words representative of analogvalues, which lookup table is read out in sequence by control processor122 and converted to analog values by an onboard digital-to-analog (D/A)converter 121, and passed to the pulsed laser transmitter 124 drivercircuit. The combination of a lookup table stored in memory 125 and aD/A converter, along with the necessary logic circuits, clocks, andtimers 127 resident on control processor 124, together comprise anarbitrary waveform generator (AWG) circuit block. The AWG circuit blockmay alternatively be embedded within a laser driver as a part of pulsedlaser transmitter 124. In an alternative embodiment, a pulse width mode(PWM) control output is provided by control processor 122, whichperforms the same function as the AWG of the first preferred embodimentin a slightly different manner. The advantage of a PWM control output isin the simplicity afforded to the design of a RISC processor which maybe used as control processor 122. PWM control outputs are typicallyfully saturated digital outputs which vary only in duty cycle or pulsewidth. The basic pulse rate may be as high as 20 MHz-100 MHz, butfiltering or integration at the control input to the pulsed lasertransmitter 124 may have a lowpass filtering effect with a 3 dB cornerfrequency as low as 0.1-10 MHz. The use of a PWM output instead of a D/Astructure means a RISC processor may be formed in a fully digitalprocess, instead of a mixed analog/digital integrated circuit process,and at a much lower cost. Were the control processor 122 to bemanufactured in a fully digital process, the A/D converter 121 shown inFIG. 6 would have to be eliminated from the chip, and either theanalog/digital feedback eliminated entirely, or the A/D converterrealized in a separate, special purpose chip. Transmit optics 126diffuses the high intensity spot produced by pulsed laser transmitter124 substantially uniformly over the desired field of view to be imagedby the modular ladar sensor unit 29 or modular ladar sensor 14. Anoptical sample of the transmitted laser pulse (termed an ARC signal) isalso sent to the detector array 130 via optical fiber. A few pixels in acorner of detector array 130 are illuminated with the ARC (AutomaticRange Correction) signal, which establishes a zero time reference forthe timing circuits in the readout integrated circuit (ROIC) 132. Eachunit cell of the readout integrated circuit 132 has an associated timingcircuit which is started counting by an electrical pulse derived fromthe ARC signal. Alternatively, the flash detector 123 signal may be usedas a zero reference in a second timing mode. Though the ARC signalneatly removes some of the variable delays associated with transit timethrough the detector array 132, additional cost and complexity is theresult. Given digital representations of the image frames, the same taskmay be handled in software/firmware by a capable embedded processor suchas data reduction processor 140. When some portion of the transmittedlaser pulse is reflected from a feature in the scene in the field ofview of the modular ladar sensor unit 29 or modular ladar sensor 14, itmay be incident upon receive optics 128, which in the case of modularladar sensor 14 are mounted with a quick connect optics mount, in thiscase a custom designed bayonet mechanical connection. Pulsed laser lightreflected from a feature in the scene in the field of view of receiveoptics 128 may be collected and focused onto an individual detectorelement of the detector array 130. This reflected laser light opticalsignal is then detected by the affected detector element and convertedinto an electrical current pulse which is then amplified by anassociated unit cell electrical circuit of the readout integratedcircuit 132, and the time of flight measured. Thus, the range to eachreflective feature in the scene in the field of view is measurable bythe modular ladar sensor 14 or modular ladar sensor unit 29. Thedetector array 130 and readout integrated circuit 132 may be an M×N orN×N sized array. Transmit optics 126 consisting of a spherical lens,cylindrical lens, holographic diffuser, diffractive grating array, ormicrolens array, condition the output beam of the pulsed lasertransmitter 122 into a proper conical, elliptical, or rectangular shapedbeam for illuminating a central section of a scene or objects in frontof the host platform as in the case of professional video camera 12, andillustrated in FIG. 1.

Continuing with FIG. 6, receive optics 128 may be a convex lens,spherical lens, cylindrical lens or diffractive grating array. Receiveoptics 128 collect the light reflected from the scene and focus thecollected light on the detector array 130. Traditionally, detector array130 has been formed on an indium phosphide semiconducting substrate witha set of cathode contacts exposed to the light and a set of anodecontacts electrically connected to the supporting readout integratedcircuit 132 through a number of indium bumps deposited on the detectorarray 130. The cathode contacts of the individual detectors of detectorarray 130 would then be connected to a high voltage detector bias gridon the illuminated side of the array. Each anode contact of the detectorelements of detector array 130 is thus independently connected to aninput of a unit cell electronic circuit of readout integrated circuit132. This traditional hybrid assembly of detector array 130 and readoutintegrated circuit 132 may still be used, but a new technology mayreduce inter-element coupling, or crosstalk, and reduce leakage (dark)current and improve efficiency of the individual detector elements ofdetector array 130. In the new preferred method, the elements ofdetector array 130 may be formed atop a substantially monocrystallinesapphire wafer. Readout integrated circuit 132 comprises a rectangulararray of unit cell electrical circuits, each unit cell with thecapability of amplifying a low level photocurrent received from anoptoelectronic detector element of detector array 130, sampling theamplifier output, and detecting the presence of an electrical pulse inthe unit cell amplifier output associated with a light pulse reflectedfrom the scene and intercepted by the detector element of detector array130 connected to the unit cell electrical input. The detector array 130may be an array of avalanche photodiodes, capable of photoelectronamplification, and modulated by an incident light signal at the designwavelength. The detector array 130 elements may also be a P-intrinsic-Ndesign or N-intrinsic-P design with the dominant carrier being holes orelectrons respectively; the corresponding ROIC 132 would potentiallyhave the polarity of the bias voltages and amplifier inputs adjustedaccordingly.

The hybrid assembly of detector array 130 and readout integrated circuit132 of the example embodiment is shown in FIG. 15, and the assembly isthen mounted to a supporting circuit assembly, typically on a FR-4substrate (not shown). The circuit assembly provides support circuitrywhich supplies conditioned power, a reference clock signal, calibrationconstants, and selection inputs for the readout column and row, amongother support functions, while receiving and registering range andintensity outputs from the readout integrated circuit 132 for theindividual elements of the detector array 130. Many of these supportfunctions may be implemented in RISC processors which reside on the samecircuit assembly. A detector bias converter circuit 144 may apply a timevarying detector bias to the detector array 130 which provides optimumdetector bias levels to reduce the hazards of saturation in the nearfield of view of detector array 130, while maximizing the potential fordetection of distant objects in the field of view of detector array 130.The contour of the time varying detector bias supplied by detector biasconverter 144 is formulated by control processor 122 based on inputsfrom the data reduction processor 140, indicating the reflectivity anddistance of objects or points in the scene in the field of view of thedetector array 130. Control processor 122 also provides several clockand timing signals from a timing core 127 to readout integrated circuit132, data reduction processor 140, analog-to-digital converters 136,object tracking processor 158, and their associated memories. Controlprocessor 122 relies on a temperature stabilized frequency reference 142to generate a variety of clocks and timing signals. Temperaturestabilized frequency reference 142 may be a temperature compensatedcrystal oscillator (TCXO), dielectric resonator oscillator (DRO), orsurface acoustic wave device (SAW). Timing core 127 resident on controlprocessor 122 may include a high frequency tunable oscillator,programmable prescaler dividers, phase comparators, and erroramplifiers.

Control processor 122, data reduction processor 140, and object trackingprocessor 158 each have an associated memory for storing programs, data,constants, and the results of operations and calculations. Thesememories, each associated with a companion digital processor, mayinclude ROM, EPROM, or other non-volatile memory such as flash. They mayalso include a volatile memory such as SRAM or DRAM, and both volatileand non volatile memory may be integrated into each of the respectiveprocessors. A common frame memory 148 serves to hold a number of frames,each frame being the image resulting from a single laser pulse. Thereare two modes of data collection, the first being SULAR, or aprogressive scan in depth. Each laser pulse typically results in 20“slices” of data, similar to a CAT scan, and each “slice” may be storedas a single page in the common frame memory 148. With each pixelsampling at a 2 nanosecond interval, the “slices” are each a layer ofthe image space at roughly 1 foot differences in depth. The 20 slicesrepresent a frame of data, and the sampling for a succeeding laser pulsemay be started at 20 feet further in depth, so that the entire imagespace up to 1000 feet in range or depth, may be swept out in asuccession of 50 laser illuminating pulses, each laser pulse responseconsisting of 20 “slices” of data held in a single frame entry. In somecases, the frame memory may be large enough to hold all 50 frames ofdata. The reduction of the data might then take place in an externalcomputer, as in the case of data taken to map an underwater surface, ora forest with tree cover, or any static landscape, where sophisticatedpost-processing techniques in software may yield superior accuracy orresolution. A second data acquisition mode is the TRIGGER mode, wherethe individual pixels each look for a pulse response, and upon a certainpulse threshold criteria being met, the 20 analog samples bracketing thepulse time of arrival are retained in the pixel analog memories, and arunning digital counter is frozen with a nominal range measurement. The20 analog samples are output from each pixel through the “A” and “B”outputs 134 of readout integrated circuit 132, which represent theinterleaved row or column values of the 128×128 pixel of the presentdesign. The “A” and “B” outputs are analog outputs, and the analogsamples presented there are converted to digital values by the dualchannel analog-to-digital (A/D) converter 136. Interleaving the outputsmeans one of the outputs (“A”) reads out the odd numbered lines of thereadout IC 132, and the other output (“B”) reads out the even numberedlines of the readout IC 132. The digital outputs 138 of the A/Dconverters 136 connect to the inputs of the data reduction processor140. The digital outputs 138 are typically 10 or 12 bit digitalrepresentations of the uncorrected analog samples measured at each pixelof the readout IC 132, but other representations with greater or fewerbits may be used, depending on the application. The rate of the digitaloutputs 138 depends upon the frame rate and number of pixels in thearray. The digital range representations from each pixel are output to acommon bidirectional digital data bus 152 and transfer thus to datareduction processor 140. In this second mode, a great deal of datareduction has already transpired, since the entire range or depth spacemay be swept out in the timeframe of a single laser pulse, and the datareduction processor 140 would only operate on the 20 analog samples ofeach pixel in order to refine the nominal range measurement receivedfrom each pixel. The data reduction processor 140 refines the nominalrange measurements received from each pixel by curve fitting of theanalog samples to the shape of the outgoing laser illuminating pulse,which is preserved by the reference ARC pulse signal. In TRIGGERacquisition mode, the frame memory 148 only needs to hold a “pointcloud” image for each illuminating laser pulse. The term “point cloud”refers to an image created by the range and intensity of the reflectedlight pulse as detected by each pixel of the 128×128 array of thepresent design. In this second mode, the data reduction processor servesmostly to refine the range and intensity (R&I) measurements made by eachpixel prior to passing the R&I data to the frame memory 148 over databus 146, and no “slice” data or analog samples are retained in memoryindependently of the R&I “point cloud” data in this acquisition mode.Frame memory 148 provides individual or multiple frames, or full pointcloud images, to control processor 122 over data bus 154, and to anoptional object tracking processor 158 over data bus 150 as requested.

Typically, data reduction processor 140 and control processor 122 are ofthe same type, a reduced instruction set (RISC) digital processor withhardware encoded integer and floating point arithmetic units. Objecttracking processor 158 may also be of the same type as RISC processors140 and 122, but may in some cases be a processor with greatercapability, suitable for highly complex graphical processing. Objecttracking processor 158 may have in addition to hardware encoded integerand floating point arithmetic units, a number of hardware encoded matrixarithmetic functions, including but not limited to; matrix determinant,matrix multiplication, and matrix inversion. In operation, the controlprocessor 122 controls readout integrated circuit 132, A/D converters136, data reduction processor 40 and object tracking processor 158through a bidirectional control bus 152 which allows for the master,control processor 122 to pass commands on a priority basis to thedependent peripheral functions; readout IC 132, A/D converters 136, datareduction processor 140, and object tracking processor 158.Bidirectional control bus 152 also serves to return status and processparameter data to control processor 122 from readout IC 132, A/Dconverters 136, data reduction processor 140, and object trackingprocessor 158. Bus 152 is also used to pass uncorrected digital rangerepresentations to data reduction processor 140. Data reductionprocessor 140 refines the nominal range data and adjusts each pixelintensity data developed from the digitized analog samples received fromA/D converters 136, and outputs a full image frame via unidirectionaldata bus 146 to frame memory 148, which is a dual port memory having thecapacity of holding several frames to several thousands of frames,depending on the application. Object tracking processor 158 has internalmemory with sufficient capacity to hold multiple frames of image data,allowing for multi-frame synthesis processes, including videocompression, single frame or multi-frame resolution enhancement,statistical processing, and object identification and tracking. Theoutputs of object tracking processor 158 are transmitted throughunidirectional data bus 156 to a communications port 166, which may beresident on control processor 122. All slice data, range and intensitydata, control, and communications then pass between communications port166 and a host platform through bidirectional connections 160 andelectromechanical interface 162. Power and ground connections (notshown) may also be supplied through electromechanical interface 162Connections 160 may be electrical or optical transmission lines, andelectromechanical interface 162 may be a DB-25 electrical connector, ora hybrid optical and electrical connector, and the mechanical interfacemay be just the mechanical structure of the DB-25 connector andassociated screws, or it may include other mechanical support andretention mechanisms, such as guide rails, retention latches, etc.Bidirectional connections 160 may be high speed serial connections suchas Ethernet, USB or Fibre Channel, or may also be parallel high speedconnections such as Infiniband, etc., or may be a combination of highspeed serial and parallel connections, without limitation to thoselisted here. Bidirectional connections 160 also serve to uploadinformation to control processor 122, including program updates for datareduction processor 140, object tracking processor 158, and globalposition reference data, as well as application specific controlparameters for the remainder of the modular ladar sensor unit 29 or 14functional blocks. Inertial/vertical reference 164 is utilized inaddition to external position references by control processor 122, whichmay pass position and inertial reference data to data reductionprocessor 140 for adjustment of range and intensity data, and to objecttracking processor 158 for utilization in multi-frame data synthesisprocesses. The vertical reference commonly provides for measurement ofpitch and roll, and is adapted herein to readout an elevation angle, anda twist angle (analogous to roll) with respect to a horizontal planesurface the modular ladar sensor unit 29 or modular ladar sensor 14and/or the professional video camera 12 may be mounted on. A hostplatform such as professional video camera 12 may have a number ofconnector receptacles generally available for receiving mating connectorplugs from USB, Ethernet, RJ-45, or other interface connection, andwhich may alternatively be used to attach a modular ladar sensor 14 ormodular ladar sensor unit 29 of the type described herein.

The use of a semiconducting laser in a preferred embodiment allows fortailoring of the drive current to a VCSEL laser, one example of asemiconductor laser, or any diode laser, so as to produce a Gaussianoptical pulse shape with only slight deviations. The VCSEL response timeis in the sub-nanosecond regime, and the typical pulse width might be5-100 nanoseconds at the half power points. In the diagram of FIG. 6,the VCSEL and laser driver would be part of the pulsed laser transmitter124, and the desired pulse or waveshape is itself produced by adigital-to-analog converter 121 which has a typical conversion rate of200-300 MHz, so any deviations in the output pulse shape from theGaussian ideal may be compensated for in the lookup table in memory 125associated with control processor 122, which serves as the digitalreference for the drive current waveform supplied to the laser driverwithin pulsed laser transmitter 124 by the D/A converter. A Gaussiansingle pulse modulation scheme works well at short ranges, given thelimited optical power available from a VCSEL laser.

The unit cell electronics depicted in FIG. 7 is well adapted to workwith the Gaussian single pulse modulation scheme of a VCSEL laser, andworks advantageously with other modulation schemes as well, includingsequences of flat-topped pulses, Gaussian, or otherwise shaped pulses.These pulses may be of varying width and spacing, in order to reducerange ambiguities, and may also be random pulse sequences, or in othercases, Barker coded pulse sequences. In operation, some portion of thepulsed laser light reflected from a surface in the field of view of themodular ladar sensor unit 29 or modular ladar sensor 14 is concentratedand focused by receive optics 128 and falls on an individual detectorelement 131 of detector array 130. The individual element 131 istypically an avalanche photodiode, but may be a PIN or NIP, or otherstructure. Each individual element 131 is biased with a voltage by abias voltage distribution network VDET 133. The reflected light signalincident upon the individual detector element 131 is converted to anelectronic signal, typically a photocurrent, and amplified by inputamplifier 172, typically a transimpedance amplifier. A current amplifiermay also be used as an input amplifier 172 with a current output drivingthe integrating capacitors of the unit cell memory cells associated witheach sampling gate, and the input current waveform thereby sampled andstored as a series of voltage samples. The output of input amplifier 172is distributed to a trigger circuit 170 as well as a number of analogsampling gates 180. Sampling is typically initiated when an illuminatinglaser pulse is transmitted, and begins with the first transition ofsampling clock 186, which may be a gated free running oscillator. Thetrigger circuit 170 is typically a threshold voltage comparator, set totrigger when a pulse is received which exceeds a predeterminedmagnitude, though other pulse detection schemes may be used. After aprogrammable delay through delay circuit 168, the circular selector 182is frozen by the logic transition of trigger circuit 170 output. Thisfirst mode of operation is called TRIGGER mode. TRIGGER mode is selectedby a global input “T” to each unit cell which comes from the commonportion of ROIC 132. Prior to the detection of a received pulse bytrigger circuit 170, the sample clock 186 causes the state of circularselector 182 to advance, enabling one of the sampling control outputsS1-S3, which in turn causes a sampling of the input amplifier 170 outputby one of the sampling gates 180. The number of transitions of sampleclock 186 are counted by counter 184, as the circular selector 182outputs a logic transition to counter 184 for every cycle of thesampling clock after the release of the active low reset line 185.Circular selector 182 may cycle through outputs S1-S3 in order, or mayhave a different order, depending on the programming. A second circularselector 182, and sample clock 186 may operate in parallel, along withcounter 184, analog sampling gates 180 and analog memory cells 178. Thecombination of sample clock 186, counter 184, circular selector 182,sampling gates 180, and memory cells 178 may be termed a unit cellsampling structure (within dashed line boundary 183) for clarity. Two,three, or more of these sampling structures may be operated in parallelon the output of input amplifier 172, with the advantages of such astructure to be described later in regards to range ambiguity. Shown inFIG. 7 are three sampling gates 180, and analog memory cells 178, butthe number may be several hundred or more on some readout ICs 132. Asecond mode of operation is called SULAR mode, wherein sampling isinitiated upon the issuance of an outgoing illuminating laser pulse, andsampling continued until all of the analog memory cells 178 are filled.When the global input “T” is deselected, the mode of operation is set toSULAR. In SULAR mode, sampling may also be initiated at a programmabledelay after the issuance of an outgoing illuminating laser pulse.Therefore SULAR mode allows the entire space in the field of view of theladar to be swept out in sequence if desired, rather than simplyfocussing on the first reflection large enough to force a transition ofthe trigger circuit 170. Once all of the analog sample data has beentaken, a control command from the control processor 122 initiates areadout cycle by activating output control 174 and output amplifier 176to readout the contents of the analog memory cells 178 in apredetermined order. Assuming a 1 cm² VCSEL array with a 5 kW/cm² powerdensity, and depending upon the reflectivity of the objects in the fieldof view of the modular ladar sensor unit 29, and the responsivity andexcess noise of the detector array 130, the effective range of aGaussian single pulse modulation scheme might be in the range of 10-20meters, using a simple threshold detection technique. Without resortingto a large VCSEL array, which might be expensive and might require avoluminous discharge capacitor to supply a massive current pulse, moresophisticated modulation and detection techniques can be used to createadditional processing gains, which effectively increase thesignal-to-noise ratio, thus extending the range of the modular ladarsensor unit 29 or modular ladar sensor 14 without requiring an increasein power. With a Gaussian single pulse modulation, a detection techniquemay be employed which uses the digitized analog samples from each unitcell electrical circuit, and processes these samples in a digitalmatched filter to find the centroid of the received pulse, resulting insignificant processing gain. The processing gains resulting from thisstructure are proportional to the square root of the number of samplesused in the filtering algorithm. For example, a unit cell electricalcircuit with 256 analog memory cells could yield a processing gain of 16if all the available analog samples were used in a matched filteralgorithm. Assuming the pulsed laser light is distributed uniformly overjust the field of view of the receive optics 128, the range alsoincreases as the square root of the transmitted power, and an increasein range to 40-80 meters could be the result.

In a second modulation scheme, a VCSEL array modulated with a series ofBarker encoded flat-topped or Gaussian pulses can be sampled by the unitcell electronics of FIG. 7 and analyzed by data reduction processor 140for range and intensity estimates. In a third modulation scheme, a VCSELarray modulated with a gated sinewave allows for greater cumulativeenergy to be reflected from a feature in a scene in the field of view ofthe modular ladar sensor unit 29 or modular ladar sensor 14 without anyincrease in peak power. Each peak of a gated sinewave will have aseparate reflection from an object or feature in the scene in the fieldof view of the modular ladar sensor unit 29 or modular ladar sensor 14,and the unit cell electrical circuit of FIG. 7 allows the ladar sensorreceiver to respond to the cumulative energy from many of thesereflected pulses using a minimum of circuitry. The waveform in apreferred embodiment is a number of sinewave cycles, and the numbercould be quite large, depending on a number of factors. The receivercircuitry of the unit cell electronics shown in FIG. 7 is capable ofsampling or of synchronously detecting the cumulative energy of thereturned pulse peaks. Two modes of sampling are supported by the unitcell sampling structure shown in FIG. 7. When taking analog samples ofsingle pulse or multi pulse sequences, wherein analog samples of anincoming waveform are being sequentially taken, the sampling impedancecontrol 173 (Z) to the circular selector 182 is set to a minimum value.The sampling frequency of sample clock 186 is also selected to produce10 or perhaps 20, analog samples during each pulse width. When thesampling impedance control 173 is set to a minimum, the sample controlsS1, S2, S3 . . . turn on with full voltage during a sampling cycle.Since each sampling gate 180 is a field effect transistor, increasingthe sample control voltage S1-S3 will increase the gate-source voltageon the sampling FET, thus lowering the resistance of the channel betweensource and drain, and setting the sampling gate 180 series resistance toa minimum. When the sampling gate 180 impedance is set to a minimum, thestorage capacitor serving as analog memory cell 178 charges rapidly tothe voltage present at the output of input amplifier 172. This mode canbe termed “instantaneous voltage sampling” to distinguish the mode froma second sampling mode, which is selected when the sampling impedancecontrol 173 is set to a higher, or even maximum value. When the samplingimpedance control 173 is selected for high impedance, or maximum seriesresistance value, the outputs S1-S3 would be at or near minimum voltageswhen enabled, resulting in a lower gate-source voltage across each ofthe sampling gate FETs 180, and thus a higher sampling gate seriesresistance in the channel between source and drain of each sampling gate180 FET. With the series resistance of the sampling gates 180 set tohigh or maximum value, the effect is to cause an R-C filter to develop,with the analog memory cell 178 storage capacitor performing as anintegrating capacitor. This second sampling mode may be very useful whena sinusoidal modulation is applied to the pulsed laser transmitter 124in the case where the laser is a semiconductor laser, typically a highefficiency VCSEL. By applying a sampling clock 186 through the S1 outputto the sampling gate 180, and which is the same frequency as thesinusoidal modulation, a sum frequency and a difference frequency willbe in the sampled signal, and the analog memory cell 178 storagecapacitor will filter out the sum frequency, and the differencefrequency will be zero, leaving only a DC voltage component representingthe phase difference remaining Over a number of cycles of the sinusoidalmodulation from the output of input amplifier 172, this DC voltage willemerge as the sine or cosine of the phase difference. This phasedifference is proportional to the range to a reflecting surface. Toimprove the processing gain, the second sampling gate driven by the S2signal is driven by the same sampling clock frequency, but shifted by 90degrees in phase, and the greater of the two DC voltages, or a ratio ofthe two voltages, may used to estimate phase, and thereby range.Typically, a ratio of phase measurements is preferred, since iteliminates amplitude variations in the return signal as an error term.In this second sampling mode, circular selector 182 acts to pass thesampling frequency present at the Fs input straight through to the S1output, and a 90° phase shifted copy of Fs to the S2 output. A thirdphase shifted version of the sampling frequency Fs, perhaps a 45 degreephase shifted copy of Fs, may be passed through to the S3 output, and soon until each sampling gate 180 in the unit cell sampling structure 183has a copy of the Fs sampling clock frequency signal, each with a uniquephase. Alternatively, all of the sampling gates 180 may be supplied onlywith 0° and 90° phase shifted copies of the Fs sampling frequency. Ineither case, the results read out from the memory cells 178 may becombined externally in the data reduction processor 164 to achievesignificant processing gains. Thus, the sampling gates 180 can beoperated as instantaneous voltage samplers in a first sampling mode, oras frequency mixers in a second sampling mode, depending on the state ofthe sampling impedance control 173, and the frequency applied bysampling clock 186. In the first sampling mode, the shape of a pulse orsequence of pulses may be acquired, and in second sampling mode, aperiodic waveform modulation such as a sinewave, may be demodulatedthrough the frequency mixing effect and integration on a storagecapacitor, resulting in a phase measurement and thereby, a rangeestimate. In a third modulation case, two and perhaps three sinewaves ofdifferent frequencies are superimposed as a modulation signal on asemiconductor laser, and the received waveform output from inputamplifier 172 is sampled by 2 or 3 unit cell sampling structuresarranged in parallel, and operating at the 2 or 3 different frequenciesof the modulation signal. Each frequency is demodulated and the phasemeasured by the unit cell sampling structure 183 tuned to the frequencyof interest by feeding the appropriate sampling frequency from sampleclock 186, typically a copy of the modulation frequency.

When measuring the phase of reflected laser energy with respect to atransmitted laser sinewave modulation, certain limits must be observed.If the ladar should have a maximum range capability of 150 meters infree space, the total round trip delay from transmit to receive would bearound 1 microsecond. For the phase measurement to be meaningful, thefrequency of transmission must therefore be less than 1 MHz to avoidspatial (distance) aliasing of targets at the 150 meter limit. In otherwords, the further the target, the lower the frequency of modulationmust be for a single modulation frequency phase measurement to bemeaningful. In a conventional sweep radar, the dwell time on the targetis limited, so return signals beyond the maximum design range often donot appear as aliased, or “ghost” signals at a shorter apparent range.In the ladar of the instant invention, the typical mode is a staringmode, and there is no sweep of the illuminating beam or receivingantenna across the target space. Therefore, in the modular ladar sensorunit 29 or modular ladar sensor 14 of the present design, responses fromtargets beyond the designed maximum range could produce an aliasedresponse (one in which the phase shift is greater than 2π). A method forresolving these aliased, or “ghost” images is to illuminate the targetin a second or third transmission with a slightly different frequency;for example 0.99 MHz versus the 1.0 MHz in a first gated sinewaveilluminating pulse. If the target image remains at the same apparentrange, it is likely a real target at a range less than the designmaximum range limit. If the apparent range of the target shifts at thesecond illuminating frequency, it is likely the image is an aliased, or“ghost” image from a target at a distance beyond the design maximumrange of the modular ladar sensor unit 29 or modular ladar sensor 14.The modular ladar senso unit 29 or modular ladar sensor 14 of theinstant invention makes use of a frequency agile transmitter which canrapidly tune from a first transmission frequency to a secondtransmission frequency, and more if necessary. In one preferredembodiment, the unit cell sampling structure is doubled or tripled, andoperated in parallel, and two or three sinewave modulation signals aresuperimposed on a semiconductor laser transmitter. When using multiplefrequency modulation, the individual frequencies should not be simpleharmonics of each other; i.e., they should not be related by fractionsof low value integers. The modular ladar sensor unit 29 or modular ladarsensor 14 of the preferred embodiment may make use of a semiconductorlaser, typically a VCSEL structure, enabling the use of shaped singlepulses, shaped multiple pulses, shaped and encoded multiple pulses,gated sinewave, gated chirped sinewave, and multi-frequency gatedsinewave modulation schemes. By selecting a modulation regimeappropriate to the particular scene or objects to be imaged, theflexible modulation capabilities of the present design result in aminimum sized pulsed laser illuminating source with maximum performancein range and resolution.

FIG. 8 illustrates a feature of the multi-camera production system asshown in FIGS. 1 and 2. In order to make sure the 3-D images returnedfrom each modular ladar 14 or 29 are coincident in time with another 3-Dimage, each frame of video or still picture is time stamped byproduction video camera 12, 28, 32, or 38. For a moving target, it isimportant when synthesizing 3-D models of the scene in the field ofview, to have the images taken at the same time. This time stampreference information can come from a GPS receiver if one is embedded orattached to the individual camera 12, or it may be distributed locallyover the connecting fiber optic cable 8, or electrical cable 36 or bylocal wireless transmission. In a GPS denied environment, or when lowercost cameras are being used without GPS antennas and receivers, mastercontrol console 46 may distribute a local time reference via theconnecting fiber optic 8 and electrical cables 36, and may nullify thedifferences in cable length by several means. The master control console46 has a clock and timing control 194, which may send out a command tocamera module 1 (12) indicating a cable length measurement sequence isforthcoming, followed by an outbound timing pulse, with the pulse beingapplied to a small semiconductor laser at a first wavelength, 1300nanometers. The outbound timing pulse, at a first wavelength of 1300nanometers is coupled to fiber optic cable 8 by wavelength multiplexer188. Fiber optic cable 8 has a male plug connector 192 at both ends,typically a SC, LC, FC, or ST type. Master control console 46 has apanel mounted female receptacle fiber optic connector 190 of the matingSC, LC, FC, or ST type which makes optical connections with the fiberoptic cable 8. At the far end of fiber optic cable 8 camera module 1(12) also has a panel mounted female receptacle connector 190 of themating SC, LC, FC, or ST type. When the timing pulse from clock andtiming control 194 is received by professional video camera 12, it isrouted to Media Access Controller (MAC) 202 and to pulse reflector 206by wavelength multiplexer 204. The timing pulse is wider than aconforming data pulse, and is ignored by the MAC, but is detected andreflected immediately by the pulse reflector 206. The reflected timingpulse is applied to a second semiconductor laser at a second wavelengthof 1345 nanometers at the wavelength multiplexer 204 and sent back downthe fiber optic cable 8. When the timing pulse is received back at thewavelength multiplexer 188 of the master control console, it is routedto clock and timing control circuit 194 which has an internal high speeddigital counter timing the process, thus measuring the two-wayelectrical delay of the fiber optic cable 8. Once the cable electricallength is known, the master control console 46 uses this information tosynchronize the real time clocks 207 in each camera module. The mastercontrol console polls a particular camera module 12 for the status ofthe real time clock 207, which request has the highest priority, andmust be responded to immediately, and with a known delay. This responsefrom the real time clock 207 should be the value of the master real timeclock 209 plus the measured delay through the cable and the fixedelectrical delays through the camera module which are known and recordedin the particular camera module. If the response from the real timeclock 207 is not as expected, an error/adjustment value is sent frommaster control console 46 to the camera module 12, and the processrepeated until the deviation/error is within acceptable bounds andperiodically checked during the dead time between camera flashes. Tocreate 3-D models accurate to a millimeter when the target may be aspeeding bullet or cannon round travelling at 3000 fps, it is necessaryto synchronize the real time clocks 207 of the several camera modules toless than 1 microsecond. All communications from master control console46 to the several camera modules over fiber optic cables are transmittedon the first wavelength, 1300 nanometers, and image and status datareceived from the camera modules on a second wavelength at 1345nanometers. Other wavelengths may be used with the same beneficialeffects.

The same cable length measuring process and real-time clock adjustmentcan be performed on electrical cable 36. The master control console hasa clock and timing control 194, which may send out a command to cameramodule 3 (38) indicating a cable length measurement sequence isforthcoming, followed by an outbound timing pulse, with the pulse beingapplied to a high frequency gated oscillator, producing a 2 gigahertz RFpulse. The outbound timing pulse, at a first frequency of 2 GHz iscoupled to electrical cable 36 by frequency multiplexer 196. Electricalcable 36 has a male plug connector 200 at both ends, typically a BNC,RJ-45, TNC, HSSDC, DB-9 or other connector well suited to the particularcable type. Master control console 46 has a panel mounted femalereceptacle electrical connector 198 of the mating BNC, RJ-45, TNC, orDB-9 type which makes electrical connections with the electrical cable36. Other cabling and connector types may be used without significantlyaltering the operation and benefits of the instant invention. At the farend of electrical cable 36 camera module 3 (38) also has a panel mountedfemale receptacle connector 198 of the mating BNC, RJ-45, TNC, or DB-9type. When the timing pulse from clock and timing control 194 isreceived by professional video camera 38, it is routed to Media AccessController (MAC) 202 and to pulse reflector 206 by frequency multiplexer208. The timing pulse is wider than a conforming data pulse, and isignored by the MAC, but is detected and reflected immediately by thepulse reflector 206. The reflected timing pulse is applied to a secondhigh frequency gated oscillator at a second frequency of 250 MHz at thefrequency multiplexer 208 and sent back down the electrical cable 36.When the timing pulse is received back at the frequency multiplexer 196of the master control console, it is routed to clock and timing controlcircuit 194 which has an internal high speed digital counter timing theprocess, thus measuring the two-way electrical delay of the electricalcable 36. The master control console 46 then is able to synchronize thereal time clock on camera module 3 (38) in the same manner as describedwith respect to camera module 1 (12), by polling the real time clock 207of camera module 3 (38) and making error measurements and adjustmentsuntil the real time clock 207 error is within acceptable limits. Allcommunications from master control console 46 to camera modulesconnected via electrical cables are transmitted on the first frequency,2 Ghz, and image and status data received from the camera modules on asecond frequency of 250 MHz. Other frequencies and electrical modulationschemes may be used with the same beneficial effects. An alternativesignaling scheme may use time division multiplexing over one fiber witha first wavelength of λ1 or electrical cable with frequency λ2 used tohandle two-way data communications and control, with handshakingcontrolled by the media access controller 186 resident on the mastercontrol console 46. The second wavelength λ2 or frequency f2 may be usedsolely for the cable length measurement function. A third alternativesignaling scheme makes use of time division multiplexing over one fiberwith a first wavelength of λ1 or electrical cable with frequency f1 usedto handle two-way data communications and control, with handshakingcontrolled by the media access controller 189 resident on the mastercontrol console 46. No second wavelength λ2 or frequency f2 is required.In this case, cable length measurement is managed by the use of specialcontrol codes or non-compliant data pulses which are recognized by theterminal end MACs 202. For instance, all data fields may be 8B/10Bencoded, which encodes 256 data words into a space with 1024 possiblecombinations, leaving 768 codes available for special status reportingor control functions such as cable length measurement.

Shown in FIG. 9 is a bidirectional wavelength multiplexer of the typereferenced in FIG. 8 as 188 and 204. An enclosure 210 is typically madeof deep drawn or formed Covar®, a steel alloy with a thermal coefficientof expansion matched to the TCE of the glass seals 214 whichelectrically insulate beryllium copper or Covar® leads 212, and seal thepackage against the environment. An insulating substrate 216, typicallyalumina or aluminum nitride, is mounted to the inner surface of theenclosure 210 which has a metalized top surface 218 connected to a lead212 via wirebond 220. Bonded to the top of insulating substrate 216 isdetector diode 222, typically a gallium arsenide PIN structure. Inoperation, detector diode 222 receives light reflected from dichroicbeamsplitter 232, which reflects light at a first wavelength λ1,typically 1300 nm in the case of the wavelength multiplexer 204 embeddedin the various camera modules 12, 38, etc. of the preferred embodiment,and passes other wavelengths only slightly attenuated. A precisionreceptacle sleeve 224 is welded to, or formed with enclosure 210, and aferrule stop 230 formed integrally with enclosure 210, or weldedthereto. Within sleeve 224 is bonded a short section of a precisioncylindrical ferrule 228 with a centered bore containing a short sectionof polished optical fiber 226. The ferrule 228 and fiber 226 mate with asimilar ferrule from the plug end of a mating fiber optic connectorplug, when the tip of the mating connector ferrule is inserted into thesleeve 224. When properly mated, the ferrule 228 and polished opticalfiber 226 receive and transmit optical signals bidirectionally along theaxis of rotation of optical fiber 226. Detector diode 222 may be a PIN,APD, or photovoltaic converter producing a current or voltage inresponse to illumination by an optical signal of the proper wavelength.Dichroic beamsplitter 232 is held in place by epoxy and/or a retentionfeature of enclosure 210 which may be integrally formed or attachedthereto. A vertical cavity surface emitting laser or surface emittingLED 234 is attached to a second substrate 216, and transmits opticalsignals at a second wavelength, λ2 in response to a current or voltageapplied through a second set of leads 212. The second wavelength λ2 istypically 1345 nm, but may be any wavelength which differs enough fromλ1 to allow for a practical dichroic beamsplitter 232 to easily separatethe two wavelengths of light. The assembly of FIG. 9 is commonlyreferred to as a “BIDI”, or bidirectional communications module, and iscommonly used in terrestrial fiber optic networks. At the source endembedded in master control console 46, the BIDI 188 may use beamsplitter232 unaltered, and assembled in the exact same manner, except thepositions of detector diode 222 and VCSEL or LED 234 must be reversed.In addition, the wavelength of VCSEL or LED 234 needs to be switched toλ1 at the source end BIDI 188. Detector diode 222 is typically abroadband detector, sensitive over a broad range of wavelengths,including both λ1 and λ2, so it would normally not need replacing.Master control console 46 may have one source end BIDI 188 for eachcamera module served by fiber optic connections.

FIG. 10 is a diagram of the frequency multiplexer 196 referenced in FIG.8. An input RF connector 236 makes connection to an input RF cableconnector, and to a controlled impedance microstrip line 237. A coupledline segment 238 is typically one quarter wavelength in length and isused to direct the higher frequency f1, at 2 GHz in the preferredembodiment, to a bandpass filter 240 and an upper band output connector246. The lower band frequency f2, typically at 250 MHz, is passedthrough to lower band output connector 244. The lower band output 244may be filtered through a low pass or bandpass filter (not shown) beforebeing connected to MAC 202 or pulse reflector 206 in the example of FIG.8. The isolated port is terminated in a 50 ohm load 242 to ground. Otherimpedances may be used, and connectorless connections may be made atinput/output ports, and other types of couplers, tuned filters, ortransformer coupled lines may alternatively be used to the same effectwithout substantially altering the benefits of the invention. Thestructure is reversed at the source end to enable downlinkcommunications at the second frequency, f2.

FIG. 11 is a tabular representation of a file format 248 which may beused to facilitate multi-camera 3-D productions which allow for 3-Dcomputer modeling of a solid object to be constructed with a minimum ofdifficulty. In the columns of the table are the (x,y) coordinates of thedetector array, in this case x=1-128, and y=1-128. For each (x,y)coordinate pair, a 12 bit representation of range, and a 12 bitrepresentation of intensity are stored. The range number is a counteroutput which may be adjusted for a number of system non-linearities,and/or offset errors, or may be output in raw form for diagnosticpurposes, or for external data processing. The intensity number is thedigital output of an analog-digital converter which may be corrected forsystem non-linearities and initial offsets, or may be output in rawform, suitable for diagnostic purposes and post processing. In the fileheader, a number of important parameters are recorded which areessential to rapidly reducing the data from multiple ladar sensors intoa composite 3-D solid model of a scene and objects in the common fieldof view as pictured in FIG. 1. The file header includes a time stamp forthe start of a scene capture sequence, typically the real time when theflash detector 123 transitions or the moment when the ARC signal pulses.If the camera module 12 or modular ladar sensor 14 or modular ladarsensor unit 29 is equipped with a GPS receiver, the GPS locationcoordinate references are also stored, or longitude, latitude, andelevation which have been provided by a surveyor's mark and carefulmeasurement may alternatively be recorded. In addition, other elementscomprising the “pose” of the camera are stored; the elevation angle(pitch), twist angle (roll), and azimuth (yaw). Azimuthal data may berecovered from shaft encoders which are attached to the horizontal pivotmount on camera module 12 or modular ladar sensor 14 or modular ladarsensor unit 29.

FIG. 12A is a diagram showing the structures which enable modularassembly of the components comprising the modular ladar sensor 14 whichis also shown as an assembled unit in FIG. 4. A metallic shell 56encloses a number of electrical contacts, and in some variants, opticalconnector components, and is typically part of a DB-25 male connectorplug. Flange 60 provides a mechanical retention and mounting feature forthe modular ladar sensor 14, and has clearance holes for screws 58.Screws 58 may be held within the mounting holes of flange 60 by smallsheet metal clips (not shown). A bayonet style optical receiver coupling62 is adapted to receive a bayonet style optical plug coupling 262 atthe mating end of modular lens assembly 64. Bayonet style opticalreceiver coupling 62 has a bayonet receptacle feature 250 which is shownin detail in FIG. 12B. An insertion slot 254 connects to a ramped slot256, which leads into a retention détente 258. Leaf spring 260 acts tourge button catch 252 forward into détente 258 once the modular lensassembly 64 is inserted and rotated into position. Button catch 258 is ashort round column machined into the surface of the mating cylinder ofoptical plug coupling 262, or welded thereto. Modular lens assembly 64is typically cylindrical, and may be of fixed focal length, or mayalternatively be a zoom lens, and may have an internal shutter, and mayhave a motorized zoom drive. A laser transmitter module 270 is mountedto a simple header type electrical connector receptacle 264 protrudingfrom the receiver module housing 263. The electrical connectorreceptacle 264 is typically a keyed connector, which may only be matedin one orientation. Receiver module housing 263 contains all theelements of the modular ladar sensor 14 except the light collecting andfocusing lens assembly 64, and the laser transmitter 270. The receivermodule housing 263 features electrical and mechanical interfaces tosupport quick connection of a modular lens assembly 64 as well as alaser transmitter module 270. Laser transmitter module 270 is secured tothe body of receiver module 263 by four screws 268 mounted throughclearance holes in flange 266. Within flange 266 is a recessed matingconnector plug (not shown), and both receptacle 264 and the recessedmating connector plug within flange 266 may be provided with matingelectrical contacts as well as mating optical connector contacts (notshown), and are typically keyed to ensure properly oriented mating. Anoptical transmission aperture and diffusing lens 272 may be a fixedtype, or may be selectable, or continuously variable in field of viewand focal length. One of the great advantages of the modular ladarsensor 14 construction consists in the ability to isolate the productionyields of the laser transmitter module 270 assembly from the productionyields of the receiver module 263. Another advantage of the modularconstruction is the rapid configurability; larger telephoto lensassemblies 64 with long focal lengths and narrow fields of view, can berapidly interchanged with much smaller short focal length and wide fieldof view lens assemblies 64 near the end of the production line, or evenin the field. Similar advantages accrue to the modular ladar sensor 14in the use of a laser transmitter module 270, which may be a verypowerful 4 milliJoule solid state optically pumped rod laser, or a muchless powerful array of semiconductor lasers for shorter rangeapplications.

FIG. 13 shows a cross-sectional view of a new type of detector array 130which may be mated with a readout integrated circuit (ROIC) 132 as shownin FIG. 6. Of special interest in detector arrays of this type and size,is the inter-element isolation of the individual detector elements ofthe detector array 130. In the prior art flash ladar sensors describedin earlier patent applications by Stettner, et. al., the detectors areavalanche photodiode (APD) or p-intrinsic-n (PIN) detectors formed in athin gallium arsenide film atop a semi-insulating indium phosphidesubstrate. Because of the close proximity of the detector elements,which are typically spaced on a 40-100 micron pitch, and with individualdetector elements having 30-75 micron active regions, in some cases onlya 10-20 micron gap separates individual elements of the detector array130. This level of intimacy between detector elements leads tointer-element coupling both optically and electrically through theconnecting substrate and through capacitive effects. The new structuredepicted in FIG. 13 addresses these issues by starting with anelectrically insulating sapphire substrate 274. Lens elements 276 areformed over the active area of each element of the detector array 130 bywet or dry etching the prepared substrate 274 which has been coated witha photoresist and exposed to UV light. The lens elements may also beformed of a polymer material molded over the top of the sapphiresubstrate, though the substrate must be accurately registered within themold to make sure the optical axes of both lens 276 and detectorelements of detector array 130 are in line. Because the melting pointsof polymers suitable for lenses 276 are relatively low, the overmoldingof lenses 276 would typically follow, rather than precede the formationof the active detector elements of detector array 130. In the preferredmode, lenses 276 are formed in sapphire by etching of the substrate 274,and a thin film of n+ or n++ silicon 288 grown atop sapphire substrate274. N+ or n++ region 288 may also serve as precursor to an ohmiccontact being formed. A somewhat thicker absorption layer of n-silicon286 would then be epitaxially grown atop the cathode region formed bythe n+ region 288. Next, an n− silicon layer 284 is grown epitaxially,which may function as an acceleration/multiplication region when thedevice is operated under applied voltage bias. A silicon intrinsic layer282 is then grown epitaxially, which serves as an avalanchemultiplication region for the device. Finally, a p+ or p++ siliconregion 280 is grown, which serves as the device anode. Boron andaluminum may be used as dopants for any of the p-type silicon epitaxiallayers. Phosphorus, arsenic, and antimony may be used as dopants for anyof the n-type silicon epitaxial layers. Mesas are then formed in thedevice, typically at a 60 degree angle, by dry or wet etching, clearthrough the silicon, exposing the sapphire, and fully isolating eachmesa structure. The sapphire acts as an etch stop, given the properchoice of etchant. Ohmic contacts 290 are then formed by deposition oftitanium/platinum/gold, or other suitable metallization schedule, and inthe troughs between mesas, and abutting the sides of an n+ or n++ region288, making electrical contact to all of the cathodes of the individualdetector elements of detector array 130. Anode contacts 278 are alsodeposited at the same time atop each mesa structure, with thetitanium/platinum/gold metallization also being preferred. A thindielectric layer 292 of silicon nitride is then deposited in the troughsbetween detector mesas, which acts as an insulating cap layer overcathode contacts 290, and also acts as a dielectric, creating localizedcapacitance when metallic ground contacts 294 are deposited. The cathodecontacts 290 may be formed as an interconnected mesh pattern, withsquare openings for the mesa structures of the individual detectorelements of detector array 130, which protrude therethrough. The groundcontacts 294 may also form an overlying mesh pattern atop cathodecontacts 290, and the combination of cathode contacts 290, groundcontacts 294, and dielectric layer 292 may be termed a capacitivevoltage distribution grid, because it is typically used to distributethe bias voltage to the individual detector elements of detector array130. A second insulating/cap layer 296 of silicon nitride is thendeposited selectively, passivating the metallization layers and portionsof the silicon epitaxial regions. Because silicon avalanche photodiodestypically have secondary emission of photons, the isolation betweenindividual detector elements of detector array 130 is not assured. Forthis reason, a photon absorbing buffer region 298 is deposited in thegaps between detector mesas, and in the preferred embodiment, a polymerloaded with very fine carbon particles. These carbon particles may bevery fine submicron carbon particles. In some designs, a thin layer ofcrystalline aluminum nitride (AlN) 275 may be grown atop sapphiresubstrate 274 before further growth of silicon layers 288, etc. The thinlayer of AlN 275 may prove beneficial as an optical index matchinglayer, serving to reduce optical reflections at the sapphire-siliconinterface. Other insulating substrate materials may be used, butsapphire is well matched to silicon for single crystal epitaxial growth,desirable for the detector elements of detector array 130. Othermetallization schemes may be used, though the titanium/platinum/gold ispreferred. Materials other than carbon may also be used as a photonabsorbing buffer, without any significant changes to the benefits of thedescribed device. The choice of silicon as a detector material wouldimply a shift in illuminating wavelength to a range between 400-1100nanometers, and this may be desirable in certain applications, and maybe accommodated by a solid state Nd:YAG laser at 1064 nm or asemiconductor laser of InGaAsP at any wavelength between 780-1000 nm.

In order to function as a photodetector at the preferred wavelength of1.57 microns, the structure of FIG. 13 may be adapted to use galliumnitride or indium gallium nitride as a replacement for silicon in any ofthe five semiconductor layers of the mesa structures shown in FIG. 13.Gallium nitride is also a good match for sapphire substrates with theproper crystal plane orientation. GaN on sapphire is commonly used tocreate high brightness blue and UV lasers and LEDS in volume forBlu-Ray® disc players, and lighting, respectively. The steps toconstruct the an APD device from GaN would be the same as thosedescribed with respect to the silicon APD structure of FIG. 13, exceptsubstituting GaN for silicon in each epitaxial growth. Silicon andgermanium may be used as dopants for any of the n-type GaN layers. Insome cases, magnesium may be used as a dopant for any of the p-typelayers in GaN. The photon absorbing buffer layer 298 is not necessary,and may also be eliminated, since the material would be GaN, which doesnot exhibit a secondary photon emission phenomenon.

FIG. 14 shows a cross section view of a p-intrinsic-n (PIN) detectorarray 130 created from a GaN on sapphire wafer. The structure is thesame and the processing similar to the processing as described withrespect to FIG. 13, except the two n− layers 286 and 284 are eliminated,and the photon absorbing buffer layer 298 is not necessary since thematerial is GaN, which does not exhibit a secondary photon emissionphenomenon. Instead, the n+ cathode 300 is grown from gallium nitride,the intrinsic layer 302 is GaN, and the p+ anode 304 is grown from GaNas well. In some designs, a thin layer of lattice-matched crystallinealuminum nitride (AlN) 275 may be grown atop the sapphire substrate 274before further growth of GaN layers 300, etc. The thin layer of AlN 275may prove beneficial as an optical index matching layer, serving toreduce optical reflections at the sapphire-gallium nitride interface.The PIN detector structure of FIG. 14 offers somewhat betteruniformities in individual detector characteristics across the detectorarray 130 (albeit at less than unity gain), lower processing complexity,and better yields, and therefore is preferable in some applicationswhere the superior performance of an APD is not required. Two detectorstructures for a detector array 130, one with PIN detectors, and theother with APD detectors, are shown in FIGS. 13 and 14, which are formedon an insulating sapphire substrate, isolated via an etch back to thesupporting sapphire substrate, and may be made from either silicon orGaN, and which have a capacitive voltage distribution grid, to furtherreduce the degree of inter-element coupling.

FIG. 15 is a diagram showing the mating of detector array 130 withreadout IC 132. Row amplifiers 306 and column amplifiers 314 allow theoutput from a unit cell electrical circuit 308 to be output as part of arow output or column output read cycle. All signals to and from readoutIC 132 are communicated through bond pads 312 at the periphery of theROIC 132. Atop each unit cell electrical circuit 308 is an indium bump310 which is compressed and deformed under temperature and pressure aspart of the bonding process which mates detector array 130 to readout IC132. The indium bump 310 may instead be a low temperature solder bump,which may be reflowed to permanently bond detector array 130 to readoutIC 132. The arrow shows the direction of mating, and the top of detectorarray 130 shows the grid pattern of a microlens array comprised of lenselements 276 which collect and focus light into each of the individualdetector elements of detector array 130 formed on the anterior surface.

Having now described various embodiments of the disclosure in detail asrequired by the patent statutes, those skilled in the art will recognizemodifications and substitutions to the specific embodiments disclosedherein. Such modifications are within the scope and intent of thepresent disclosure as defined in the following claims.

What is claimed is:
 1. A modular ladar sensor comprising: a receivermodule within a housing, said housing having a quick connect opticalreceiver coupling, said housing further having a laser transmitterelectrical connector and a laser transmitter mechanical mount forrapidly mounting a laser transmitter module; a lens assembly with aquick connect optical plug coupling which mates with said opticalreceiver coupling; a laser transmitter module with an electricalconnector adapted to engage and mate with said laser transmitterelectrical connector, and with complementary mechanical mounting andfastening features which mate with said laser transmitter mechanicalmount, said laser transmitter with a modulated laser light output and adiffusing optic for illuminating a scene in the field of view of saidmodular ladar sensor; a two dimensional array of light sensitivedetectors positioned at a focal plane of said lens assembly, each ofsaid light sensitive detectors with an output producing an electricalresponse signal from a reflected portion of said modulated laser lightoutput; a readout integrated circuit with a plurality of unit cellelectrical circuits, each of said unit cell electrical circuits havingan input connected to one of said light sensitive detector outputs, eachunit cell electrical circuit having an electrical response signaldemodulator and a range measuring circuit connected to an output of saidelectrical response signal demodulator, said range measuring circuitfurther connected to a reference signal providing a zero range referencefor the said range measuring circuit; and, a detector bias circuitconnected to at least one voltage distribution grid of said array oflight sensitive detectors, and a temperature stabilized frequencyreference.
 2. The modular ladar sensor of claim 1 wherein said quickconnect optical receiver coupling comprises a bayonet style mount. 3.The modular ladar sensor of claim 1 wherein said laser transmitterelectrical connector is a keyed connector.
 4. The modular ladar sensorof claim 1 wherein said laser transmitter electrical connector furthercomprises optical connector contacts.
 5. The modular ladar sensor ofclaim 1 wherein said complementary mechanical mounting and fasteningfeatures are comprised of clearance holes and screws.
 6. The modularladar sensor of claim 1 wherein said modulated laser light outputcomprises pulsed laser light.
 7. The modular ladar sensor of claim 1wherein said modulated laser light comprises sinewave modulated laserlight.
 8. The modular ladar sensor of claim 1 wherein said array oflight sensitive detectors is formed on a semiconductor film on asapphire substrate.
 9. The modular ladar sensor of claim 8 wherein saidsapphire substrate further comprises a microlens array.
 10. A modularladar sensor unit with a field of view and a wavelength of operation,said modular ladar sensor unit further comprising: a laser transmitterwith a modulated laser light output and a diffusing optic forilluminating a scene in the field of view of a modular ladar sensor, anda two dimensional array of light sensitive detectors positioned at afocal plane of a light collecting and focusing system, each of saidlight sensitive detectors having an output producing an electricalresponse signal from a reflected portion of said modulated laser lightoutput, a readout integrated circuit with a plurality of unit cellelectrical circuits, each of said unit cell electrical circuits havingan input connected to one of said light sensitive detector outputs, anelectrical response signal demodulator, and a range measuring circuitconnected to an output of said electrical response signal demodulator,and said range measuring circuit further connected to a reference signalproviding a zero range reference for said range measuring circuit; adetector bias circuit connected to at least one voltage distributiongrid of said array of light sensitive detectors, and a temperaturestabilized frequency reference; a communications port providing rangedata from said range measuring circuits of said unit cell electricalcircuits; and, a keyed electrical connector connected to saidcommunications port and quick connect mechanical mount having at leastone mating pair of electrical contacts for connection to a hostplatform.
 11. The modular ladar sensor unit of claim 10 wherein saidlaser transmitter comprises an optically pumped solid state laser formedin a gain medium selected from the set of yttrium aluminum garnet,erbium doped glass, neodymium doped yttrium aluminum garnet, and erbiumdoped yttrium aluminum garnet.
 12. The modular ladar sensor unit ofclaim 10 wherein said laser transmitter comprises a vertical cavitysurface emitting laser formed in a semiconducting gain medium with atleast one element selected from the set of indium, gallium, arsenic,phosphorus.
 13. The modular ladar sensor unit of claim 10 wherein saidmodulated laser light output is modulated with a waveform selected fromthe set of a single Gaussian pulse profile, multiple Gaussian profilepulses, a single flat-topped pulse profile, multiple flat-topped pulses,a pulsed sinewave, and a chirped sinewave pulse.
 14. The modular ladarsensor unit of claim 13 wherein said waveform is a sequence of pulsesand said sequence of pulses are encoded using a Barker code.
 15. Themodular ladar sensor unit of claim 10 wherein said two dimensional arrayof light sensitive detectors is mounted directly to said readoutintegrated circuit.
 16. The modular ladar sensor unit of claim 10wherein said two dimensional array of light sensitive detectors isformed on a sapphire substrate.
 17. The modular ladar sensor unit ofclaim 10 wherein said two dimensional array of light sensitive detectorsis formed of a semiconductor having at least one element selected fromthe set of silicon, indium, gallium, arsenic, phosphorus, aluminum,boron, antimony, magnesium, germanium, and nitrogen.
 18. The modularladar sensor unit of claim 10 wherein said electrical response signaldemodulator comprises: an input amplifier with an output connected to atrigger circuit; a series of analog sampling gates, each sampling gatewith an associated analog memory cell, a sample clock controlling thetiming of each of said sampling gates, a selector for selecting each ofsaid sampling gates in sequence, a counter for counting the number ofsamples, an output amplifier with an input connected to each of saidanalog memory cells, an output control for selecting a sequence of saidanalog memory cell contents to be output through said output amplifier,and wherein an input of an analog to digital converter is connected tosaid output amplifier, an output of said analog to digital converter isconnected to an input of a digital processor and produces a sequence ofdigitized analog samples of said electrical response signal, and saiddigital processor is programmed to demodulate said electrical responsesignal by operating on the sequence of digitized analog samples using adigital processing algorithm.
 19. The modular ladar sensor unit of claim10 wherein said electrical response signal demodulator comprises: aninput amplifier with an output connected to a first input of a phasecomparator, said phase comparator having a phase reference signalconnected to a second input, and an output of said phase comparatorconnected to the input of an integrator, said integrator having anintegrator output with an output voltage proportional to the differencein phase between said first input and said second input of said phasecomparator.
 20. A 3D vision system comprising: a host platform having anelectronic enclosure with an opening; a modular ladar sensor with afield of view and a wavelength of operation, said modular ladar sensormounted in a unit to said host platform through the opening in saidelectronic enclosure and electrically connected to said host platformthrough an electrical connector and retained therein by a quick connectand release mechanical feature, said electrical connector having atleast one mating pair of electrical contacts, said modular ladar sensorunit incorporating a laser transmitter with a modulated laser lightoutput and a diffusing optic for illuminating a scene in the field ofview of said modular ladar sensor; a two dimensional array of lightsensitive detectors positioned at a focal plane of a light collectingand focusing system, each of said light sensitive detectors with anoutput producing an electrical response signal from a reflected portionof said modulated laser light outputs; a readout integrated circuit witha plurality of unit cell electrical circuits, each of said unit cellelectrical circuits with an input connected to one of said lightsensitive detector outputs, said unit cell electrical circuits eachhaving an electrical response signal demodulator and a range measuringcircuit connected to an output of said electrical response signaldemodulator, said range measuring circuit further connected to areference signal providing a zero range reference for said rangemeasuring circuit, and, a detector bias circuit connected to at leastone voltage distribution grid of said array of light sensitivedetectors, and a temperature stabilized frequency reference.
 21. The 3Dvision system of claim 20 wherein said host platform further comprisesat least one guiding feature selected from the set of guide rails, guideslots, and guide beams.
 22. The 3D vision system of claim 20 whereinsaid modular ladar sensor unit incorporates at least one guiding featureselected from the set of guide rails, guide slots, and guide beams. 23.The 3D vision system of claim 20 wherein said host platform furthercomprises a conductive cover secured to said opening in said electronicenclosure.
 24. The 3D vision system of claim 20 wherein said hostplatform further comprises a hinged conductive door designed to openinto a recessed cavity within said electronic enclosure.
 25. The 3Dvision system of claim 20 wherein an outer surface of said modular ladarsensor unit is a conductive surface.
 26. The 3D vision system of claim20 further comprising a housing which is formed from a processedmaterial selected from the set of bent sheet metal, cast metal alloy,forged metal alloy, and molded plastic.
 27. The 3D vision system ofclaim 26 wherein said housing has a surface treated by a processselected from the set of electroplating, chemical film application, zinccoating, chromate coating, evaporated metallic coating applied undervacuum, electroless plating, physical vapor deposition, sputtering, andflame spray.
 28. The 3D vision system of claim 20 wherein said hostplatform having an electronic enclosure further has an opening therein,and said opening with a conductive cover attached thereto, and aconductive gasket applied between said conductive cover and a surface ofsaid electronic enclosure.
 29. The 3D vision system of claim 20 whereinsaid host platform having an electronic enclosure further has an openingtherein, and a plurality of conductive spring fingers connecting betweena surface of said opening and a conductive surface of a modular ladarsensor unit inserted within said opening.
 30. A three dimensional videoproduction system capable of capturing three dimensional imagescomprising: a master controller and a plurality of ladar sensors, eachladar sensor having a field of view overlapping a common scene ofinterest to be imaged, each ladar sensor connected to said mastercontroller via a signal transmission cable, each ladar sensor having aninternal real time clock, and each ladar sensor time stamping anacquired three dimensional image file with the time given by said realtime clock, and a scene processor receiving three dimensional imagesfrom said plurality of ladar sensors, said scene processor producing asolid model of said common scene of interest by combining time stampedthree dimensional images received from said plurality of ladar sensors.31. The three dimensional video production system of claim 30 whereineach of said ladar sensors receives a real time clock reference signalfrom a satellite in earth orbit.
 32. The three dimensional videoproduction system of claim 30 wherein said master controller furthercomprises a master real time clock and a transmission cable lengthmeasuring system, and said master controller distributing anindividually cable length adjusted real time clock to each of said ladarsensors, and each of said plurality of ladar sensors thereby maintaininga real time clock synchronous with said master real time clock.
 33. Thethree dimensional video production system of claim 30 wherein each ofsaid ladar sensors is mounted to a two dimensional imaging device, andsaid two dimensional imaging device is further mounted to a pointingplatform with at least two angular degrees of freedom.
 34. The threedimensional video production system of claim 33 wherein said pointingplatform has a motorized pivot for each angular degree of freedom. 35.The three dimensional video production system of claim 34 wherein saidmotorized pivots work together with a controller to track an object ofinterest.
 36. The three dimensional video production system of claim 30wherein each of said ladar sensors is mounted to a two dimensionalimaging device, and said two dimensional imaging device is furthermounted to a traversing platform.
 37. The three dimensional videoproduction system of claim 36 wherein said traversing platform isselected from the set of a wheeled dolly, a wheeled cart on a track, anda wire supported overhead platform.
 38. The three dimensional videoproduction system of claim 37 wherein said wire supported overheadplatform comprises a SkyCam® overhead camera system.
 39. The threedimensional video production system of claim 30 wherein said commonscene of interest further comprises an object of interest selected fromthe set of an actor, an athlete, a vehicle, and an object in play. 40.The three dimensional video production system of claim 39 wherein saidobject of interest further has a feature marked with an attachedinfrared reflector.